Pocock 1894 Scorpions And Their Geographical Distribution

IV.

Scorpions and their Geographical Distribution. is a well-established fact that Scorpions h a v e been in existence since the Middle S i l u r i a n era. B u t , unfortunately, almost all that we k n o w of their geological history is furnished by a few specimens from beds of this a g e , and by a few more discovered in strata of the C o a l period. It is also well known that the structural differences between the recent and the carboniferous fossil forms cannot be justifiably r e g a r d e d in the light of an a d v a n c e in organisation. In fact, as h a s a l r e a d y been more than once pointed out, these animals furnish an a d m i r a b l e e x a m p l e of a persistent type of life. F r o m the persistence of structural c h a r a c t e r s , a persistence of habit m a y be inferred. At all events, there is little, if a n y , evidence that these animals, in the past d a y s of their history, h a v e e v e r g a i n e d a livelihood by means other than those e m p l o y e d at the present d a y . T h e r e is no reason for thinking that they h a v e e v e r adopted an a q u a t i c or arboreal mode of life, or h a v e e v e r been dependent upon running or leaping p o w e r s for the capture of prey or a v o i d a n c e of enemies ; nor is there a n y foundation for the belief that a n y species has e v e r been helped in the struggle for e x i s t e n c e by the assumption of a n y of those disguises of identity that are generally spoken of as protective colouration, or m i m i c r y . T h a t an a b u n d a n c e of time to become specialised into a n y number of strange forms has been g r a n t e d them, must be admitted on all hands ; but, p e r h a p s , no fact connected with the e x i s t i n g species of S c o r p i o n s so forcibly strikes the student as the wonderful closeness of the connection between the different genera that h a v e been established. T h e r e is, n a t u r a l l y , a considerable amount of structural v a r i a t i o n , if two e x t r e m e s be selected for comparison ; yet the e x t r e m e s are linked together by such a series of intermediate types that the division of the order into sharply-defined minor groups becomes a task of no small difficulty. N o w , this is h a r d l y what we should h a v e looked for in a group of such v a s t antiquity. We should rather h a v e e x p e c t e d to find the l i v i n g population of S c o r p i o n s composed of a l a r g e r , or smaller, number of more or less isolated forms, the annectent t y p e s between w h i c h would h a v e to be sought for in the records of their past geological history. B u t , considering that, for o b v i o u s reasons, there is p r a c t i c a l l y no record of Scorpion-life between the Carboniferous times and our own day, it is, perhaps, not 2 A

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surprising that such small links as found.

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we require h a v e not yet been

T h e relationship between the fossil and recent S c o r p i o n s has been s u m m a r i s e d in the classification proposed some few y e a r s back by D r . T h o r e l l . A c c o r d i n g to this s y s t e m , these a n i m a l s are divisible into t w o great g r o u p s — t h e A p o x y p o d e s , or those with pointed feet, including the S i l u r i a n Palaeophonus, and the D i o n y c h o p o d e s for the C a r b o n i f e r o u s A n t h r a c o s c o r p i i a n d the existing N e o s c o r p i i , all of which h a v e feet terminating in a couple of m o v e a b l e c l a w s . The chief distinctive feature between the t w o l a s t - n a m e d d i v i s i o n s is the situation of the median eyes in the A n t h r a c o s c o r p i i close to the front border of the c a r a p a c e , and in front of the lateral e y e s . T h i s archaic c h a r a c t e r , which is v e r y n o t i c e a b l e in the S c o r p i o n ' s r e l a t i v e s — Thelyphonus, Phrynus, and Galeodes—has not been retained by any e x i s t i n g g e n u s of S c o r p i o n s ; but, in the a b s e n c e of e v i d e n c e to the c o n t r a r y , it seems justifiable to conclude that those recent forms in which the median ocular tubercle is in the anterior half of the c a r a p a c e , a p p r o a c h the A n t h r a c o s c o r p i i more nearly than do those in which this tubercle is p l a c e d in or behind the middle of this plate. Judged by this test, the Scorpionidae constitute the most s p e c i a l i s e d g r o u p ; for in some of the g e n e r a of this f a m i l y the e y e s h a v e m o v e d b a c k far past the middle of the c a r a p a c e . In the Iuridae, Buthidae, Chactidae, etc., on the c o n t r a r y , the e y e s are in the anterior half of the c e p h a l o t h o r a c i c shield. A n o t h e r test of specialisation seems to be furnished by the form of the sternum of the c e p h a l o t h o r a x . In most S c o r p i o n s this plate is p e n t a g o n a l ; but in the majority of the Buthidae it is r e d u c e d by lateral compression to a small longitudinally triangular sclerite, a n d in the B o t h r i u r i d a e by antero-posterior compression to a t r a n s v e r s e l y elongated plate. B u t that these t w o forms of the sternum are nothing but specialisations of the p e n t a g o n a l type is shown by the fact that in the y o u n g of all S c o r p i o n s the pentagonal s h a p e p r e v a i l s . One more a p p a r e n t criterion of p r i m i t i v e n e s s m a y be mentioned. T h i s is the presence in m a n y of the Buthidae of a spur upon the fifth segment of the last two p a i r s of limbs, this s p u r being seemingly homologous with a spur w h i c h h a s been figured by T h o r e l l upon the corresponding segment of the l e g s in the Silurian Palaeophonus. Moreo v e r , it is important to note that a m o n g the genera of Buthidae that possess this spur a r e those that h a v e the s t e r n u m of the primitive pentagonal shape. In the Buthidae, then, and in no other g r o u p of S c o r p i o n s , we find g e n e r a that still retain the three a r c h a i c c h a r a c t e r s that h a v e been mentioned, n a m e l y , the forward position of the m e d i a n e y e s , the pentagonal sternum, and the so-called tibial spurs. We would s u g g e s t , too, that the presence of a greater than the normal number of lateral ocelli in some of the Buthidae m a y prove to be of interest in this connection. T h e usual n u m b e r of these o r g a n s is three on each

M A P OF THE WORLD TO ILLUSTRATE THE KNOWN G E O G R A P H I C A L DISTRIBUTION OF RECENT SCORPIONS.

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side ; but in some of the Buthidae there are as m a n y as five, and the fact that these five m a y be o b s e r v e d in genera that are not especially related points to the conclusion that the ancestors of this family possessed this number ; and this conclusion seems to be borne out by the c i r c u m s t a n c e that the nearest living a l l y of the S c o r p i o n s , namely, Thelyphonus, which we believe to be the most p r i m i t i v e of all the E p e c t i n a t e A r a c h n i d a , m a y also present five lateral ocelli on each side. 1

T h e conclusion that the Buthidae are, on the w h o l e , the most a r c h a i c of living Scorpions is borne out by a s t u d y of the g e o g r a p h i c a l distribution of these a n i m a l s ; for, as will be seen in the sequel, this family is represented by peculiar genera in all the quarters of the globe w h e r e S c o r p i o n s exist. T h e a b s e n c e of proofs of their great antiquity, which w a s referred to in connection w i t h the inter-relationships of the e x i s t i n g species of S c o r p i o n s , is also r e v e a l e d no less r e m a r k a b l y by a study of their g e o g r a p h i c a l distribution ; for in this latter respect t h e y show considerable r e s e m b l a n c e to such a r e l a t i v e l y recent g r o u p as the Mammalia. No doubt our k n o w l e d g e of the recent species of this latter class is v e r y much more complete than is our k n o w l e d g e of the A r t h r o p o d s in question ; but so far as we h a v e been able to ascertain, W a l l a c e ' s m a p of the Z o o l o g i c a l R e g i o n s of the w o r l d , if we eliminate the northern parts of the so-called Palaearctic and N e a r c t i c R e g i o n s w h e r e S c o r p i o n s do not occur, is closely a p p l i c a b l e to this group of animals. W e m a y , therefore, without further words o f preface, proceed to discuss the c h a r a c t e r i s t i c features of the v a r i o u s regions. In the Palaearctic R e g i o n the northern limit of S c o r p i o n s in E u r o p e and W e s t e r n A s i a a p p e a r s in a general w a y to be defined by the mountain-chain of w h i c h the P y r e n e e s is the western and the C a u c a s u s the eastern e x t r e m i t y . E a s t of the C a s p i a n they h a v e not been recorded north of the 40th parallel, but they are k n o w n to occur at t w o places upon this line, n a m e l y , at K a s h g a r in T u r k e s t a n , and at P e k i n in C h i n a . T h e t w o species from these localities are nearly allied to each other, and they u n m i s t a k a b l y belong to the M e d i t e r r a n e a n section of the g e n u s Buthus. F u r t h e r m o r e , a species of Buthus, with distinct Palaearctic affinities, h a s recently been recorded from S h a n g h a i . C o n s e q u e n t l y , we must conclude that the Mediterranean fauna extends from S p a i n and A l g e r i a to the coast of C h i n a , with the probable omission of the table-land of T i b e t . The southern limit of this area in C h i n a is, for w a n t of d a t a , uncertain ; but since the S c o r p i o n s of B u r m a , A s s a m , and N o r t h I n d i a are totally different from those of T u r k e s t a n , A f g h a n i s t a n , and P e r s i a , we m a y 1

Since, as Mr. Laurie has pointed out, the term Ctenophora, which I have recently assigned to the Scorpions as opposed to all other Arachnida which were called Lipoctena, is generally recognised as signifying a group of Ccelenterata, I wish to propose the terms Pectinifera and Epectinata as substitutes for the above.

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safely adopt the boundaries that a r e usually recognised as s e p a r a t i n g the Palaearctic and Oriental R e g i o n s . T h e e x a c t limits between the Palaearctic and E t h i o p i a n are also a little uncertain. M r . W a l l a c e d r a w s the line of d e m a r c a t i o n along the tropic of C a n c e r , and thus refers the northern half of A r a b i a to the former and the southern to the latter. B u t , with t w o e x c e p tions, the Scorpions that occur at A d e n , and at other parts of South A r a b i a , are either identical with S y r i a n and E g y p t i a n forms, or are v e r y n e a r l y related to them. F o r instance, Nebo, w h i c h is met with at A d e n and M u s c a t , is only known elsewhere from S y r i a a n d E g y p t ; Hemiscorpius has been obtained at A d e n and B a g h d a d ; Buthus quinque-striatus, a common E g y p t i a n species, extends to P e r i m Island and S o u t h A r a b i a , and the A l g e r i a n and E g y p t i a n P r i o n u r u s australis has been received from M u s c a t . On the other hand, the only E t h i o p i a n t y p e s which are found in S o u t h A r a b i a are a species of Scorpio and Parabuthus liosoma, w h i c h r a n g e s from E g y p t to M a s a i - l a n d . C l e a r l y , therefore, the M e d i t e r r a n e a n element in S o u t h A r a b i a far s u r p a s s e s the E t h i o p i a n , a n d the whole of this country must consequently be looked upon as part of the Palaearctic Region. In Africa it is i m p o s s i b l e to d r a w a hard and fast line until more collecting has been done. We know nothing of the species which p r e s u m a b l y inhabit the v a s t tract lying between A b y s s i n i a on the east and S e n e g a m b i a and G u i n e a on the w e s t . On the west coast of the R e d S e a , h o w e v e r , the M e d i t e r r a n e a n element is represented at M a s s o w a h and at Z a i l a , in S o m a l i - l a n d , by a v a r i e t y of the S p a n i s h and N o r t h African Buthus europaeus ; but species of the essentially E t h i o p i a n g e n u s Scorpio e x t e n d into N u b i a and A b y s s i n i a . A similar partial o v e r l a p p i n g of the two faunas occurs on the W e s t C o a s t of North A f r i c a , n a m e l y , in S e n e g a m b i a , w h i c h is the northern limit of Scorpio, and the southern limit of Buthus europaeus and Prionurus australis. We m a y , therefore, d r a w the line between these t w o regions along the 1 5 t h parallel or thereabouts. T h e following is a list of the Palaearctic g e n e r a with the known r a n g e of e a c h . T h o s e that a r e peculiar to the region are m a r k e d with an asterisk :—*Heterometrus, two species, N o r t h A f r i c a , S y r i a ; *Ncbo, two or three species, S y r i a , E g y p t , a n d A d e n ; *Hemiscorpius, B a g h d a d , A d e n ; *Iurus, one species, G r e e c e , A s i a Minor, E g y p t ; *Belisarius, one species, P y r e n e e s ; *Euscorpius, m a n y species, S p a i n a n d A l g e r i a to A s i a M i n o r ; ''Prionurus, two species, N o r t h Africa to P e r s i a and A r a b i a ; Buthus, m a n y species, N o r t h A f r i c a , S o u t h E u r o p e , P e r s i a to P e k i n ; *Butheolus, two species, S i c i l y , A r a b i a , P e r s i a ; Parabuthus, one species, E g y p t , A r a b i a . T h e E t h i o p i a n R e g i o n is v e r y rich in S c o r p i o n s , and contains a large n u m b e r of peculiar genera. It e m b r a c e s Africa south of the 1 5 t h p a r a l l e l , and M a d a g a s c a r , the two a r e a s representing distinct sub-regions. T h e African sub-region is peopled with Scorpionidae, Ischnuridae, and Buthidae. T h e following is a list of the g e n e r a : —

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(Scorpionidae) Scorpio, about half a dozen species, S e n e g a m b i a and the C o n g o to A b y s s i n i a and N y a s s a - l a n d ; Miaephonus, t w o species, Caffraria, D a m a r a - l a n d ; *OEcopeirus, t w o species, D a m a r a - l a n d , M o z a m b i q u e ; *Opisthophthalmus, many species, M o z a m b i q u e , N a m a qua-land, C a p e C o l o n y ; (Ischnuridae) *Ischnurus, s e v e r a l species, from A n g o l a and M o z a m b i q u e s o u t h w a r d s ; *Opisthocentrus, four or five species, C o n g o , T r a n s v a a l , a n d C a p e C o l o n y ; *Chiromachis, one species, M o z a m b i q u e ; (Buthidae) *Uroplectes, s e v e r a l s p e c i e s , N y a s s a land and C a p e C o l o n y ; *Lepreus, m a n y species, s o u t h w a r d s from the C o n g o and S o m a l i - l a n d ; Archisometrus, t w o species, C o n g o , N y a s s a land ; *Babycurus, s e v e r a l species, Old C a l a b a r and A n g o l a to M a s a i land ; Parabuthus, s e v e r a l species, A b y s s i n i a , B e n g u e l a , C a p e C o l o n y ; Buthus, a few species only, S e n e g a m b i a and A b y s s i n i a to Caffraria. At the present time we unfortunately h a v e no intimate knowledge of the S c o r p i o n s of M a d a g a s c a r . T w o peculiar genera of Buthidae, h o w e v e r , n a m e l y Grosphus and Tityobuthus, occur, and two species a s c r i b e d to Babycurus h a v e been r e c o r d e d ; there is also one peculiar species of Opisthocentrus k n o w n . T h e last two are African g e n e r a and the first t w o are essentially African in their affinities. It is, h o w e v e r , h i g h l y interesting to note the apparent a b s e n c e from this continental island of almost all the large African genera of Scorpionidae and Ischnuridae. T h e differences between the g e n e r a of Buthidae inhabiting A f r i c a and M a d a g a s c a r point to long separation between the two a r e a s ; while the absence from M a d a g a s c a r of the Scorpionidae s e e m s to indicate that the latter m a d e their w a y into A f r i c a after the separation h a d been effected. T h e Oriental R e g i o n offers some points of r e s e m b l a n c e to the African portion of the E t h i o p i a n ; but on the whole the t w o faunas are v e r y distinct. T h e following g e n e r a are k n o w n :—(Scorpionidae) Scorpio, s e v e r a l species, I n d i a , C e y l o n , J a v a ; *Palamnaeus, about four species, B e n g a l to B o r n e o and the P h i l i p p i n e s ; (Ischnuridae) *Iomachus, one species, S o u t h India ; Hormurus, one or t w o species, from B u r m a e a s t w a r d s ; (Iuridae) *Scorpiops, s e v e r a l species, N o r t h I n d i a , B u r m a ; *Chaerilus, s e v e r a l s p e c i e s , C a s h m e r e a n d C e y l o n to B o r n e o ; (Bothriuridae) *Timogenes, one species, S u m a t r a ; (Buthidae) Buthus, one species, I n d i a ; Isometrus, t w o species, S o u t h I n d i a , A s s a m ; Archisometrus, s e v e r a l species, India, C e y l o n , and B u r m a e a s t w a r d s ; *Charmus (Heterocharmus), three species, C e y l o n . The region seems s e p a r a b l e into t w o sub-regions, a western or Indian, containing C e y l o n and the g r e a t e r part of I n d i a , and an eastern or I n d o - M a l a y a n , extending from C a s h m e r e along the H i m a l a y a s to B u r m a , a n d thence s o u t h w a r d s and e a s t w a r d s to B o r n e o and the Philippines. C h a r a c t e r i s t i c of the Indian sub-region is the genus Scorpio, which in the I n d o - M a l a y a n sub-region has only t w o representatives, occurring in S u m a t r a a n d J a v a ; the single I n d i a n species of Buthus, too, does not a p p e a r to pass into B u r m a , while Iomachus and Charmus are not k n o w n from the east side of the B a y of B e n g a l . In

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the I n d o - M a l a y a n sub-region the genus Scorpio is almost entirely r e p l a c e d by its near a l l y , Palamnaeus, which ranges from B e n g a l to B o r n e o and the P h i l i p p i n e s . Hormurus australasia and Archisometrus mucronatus h a v e a p p r o x i m a t e l y the s a m e r a n g e as Palamnaeus, and are not known from India or C e y l o n , while the genera Scorpiops and C h a e r i l u s extend from C a s h m e r e into A s s a m , B u r m a , and T e n a s s e r i m . H e r e Scorpiops, of which one peculiar species has been recorded from the D e c c a n , r e a c h e s its limit ; but Chaerilus, which is also represented by a peculiar form in C e y l o n , p a s s e s into J a v a , S u m a t r a , and B o r n e o . T h e s e two genera are of special interest, i n a s m u c h as they are allied to the Palaearctic g e n e r a Iurus and Euscorpius, and thus indicate faunistic affinity between the Oriental and Palaearctic regions. A corresponding but rather closer affinity is indicated with the E t h i o p i a n R e g i o n by the presence of Scorpio in India and C e y l o n , and of Archisometrus over the whole Oriental R e g i o n . T h e A u s t r a l i a n R e g i o n is not easily s e p a r a b l e from the Oriental where the two are nearly contiguous. It m a y be divided into t w o sub-regions, a northern insular portion or A u s t r o - M a l a y a , and a southern continental portion or A u s t r a l i a . T h e following g e n e r a are represented :—(Ischnuridae) Hormurus, s e v e r a l species, Celebes, P a p u a , Solomon I s l a n d s , N e w C a l e d o n i a , E . A u s t r a l i a ; (Urodacidae) *Urodacus, several s p e c i e s , A u s t r a l i a ; (Bothriuridae) Cercophonius, one species, A u s t r a l i a ; (Buthidae) Isometrus, one species, E. A u s t r a l i a ; Archisometrus, about three s p e c i e s , C e l e b e s a n d F l o r e s , A u s t r a l i a ; *Isometroides, t w o species, A u s t r a l i a . T h e A u s t r a l i a n sub-region is recognisable from the A u s t r o - M a l a y a n by the presence of the genera Urodacus, Cercophonius, and Isometroides, which do not extend into the latter a r e a . T h i s A u s t r o - M a l a y a n sub-region is near akin to the Indo-Malayan. T w o species, n a m e l y Archisometrus mucronatus and Hormurus australasiae, are common to the two ; and the characteristic a l l y Oriental genus Chcrrihts is represented by a single s p e c i e s in C e l e b e s . B u t with the exception of H. australasiae, the genus Hormurus, of w h i c h there is a peculiar species in N e w C a l e d o n i a , does not a p p e a r to cross W a l l a c e ' s L i n e . T h e r e are no indigenous species of S c o r p i o n s in N e w Z e a l a n d a n d none, so far as has been a s c e r t a i n e d , in the P a c i f i c I s l a n d s . In N o r t h A m e r i c a the northern limit of S c o r p i o n s seems to be situated between the 3 5 t h and 40th parallels. T h e y thus belong to the S o n o r a n P r o v i n c e of M e r r i a m . To the west of the R o c k i e s these a n i m a l s h a v e been recorded from California a n d U t a h ; and to the east of this mountain chain they a p p e a r to extend into K a n s a s , C a r o l i n a , and V i r g i n i a . To the south, that is in Central A m e r i c a , the fauna seems to blend with that of the N e o t r o p i c a l . At all e v e n t s , we h a v e not sufficient data to enable us to define a c c u r a t e l y the limits between the two regions. C h a r a c t e r i s t i c genera of the S o n o r a n P r o v i n c e are *Uroctonus [Anuroctonus], three species, California, U t a h , V i r g i n i a ; *Hadrurus,

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one species, U t a h , C a l i f o r n i a ; *Vejovis, s e v e r a l species, C a r o l i n a , T e x a s , and U t a h ; a n d Centrurus, two or three species, from G e o r g i a , F l o r i d a , T e x a s , K a n s a s , and California. O f these Uroctonus does not a p p e a r to p a s s into M e x i c o ; but Hadrurus hirsutus e x t e n d s c e r t a i n l y as far as J a l a p a , w h i l e Vejovis is represented by m a n y s p e c i e s in v a r i o u s p a r t s of M e x i c o , but does not, so far as is k n o w n to me, spread into N i c a r a g u a or C o s t a R i c a . Consequently, we must conclude that the g r e a t e r part of M e x i c o belongs to the S o n o r a n P r o v i n c e . T h e g e n u s Centrurus, which i n h a b i t s the southern S t a t e s , seems to form part of the N e o t r o p i c a l fauna ; for it is represented by s e v e r a l species inhabiting C e n t r a l A m e r i c a , the W e s t Indies, C o l o m b i a , etc. S i m i l a r l y , Diplocentrus is c o m m o n to the two regions, since it occurs in T e x a s , M e x i c o , the W e s t Indies, and Brazil. B u t with these exceptions the N e o t r o p i c a l fauna of A m e r i c a , i n c l u d i n g P a n a m a and all the countries to the south of it, as w e l l as the W e s t Indies, is v e r y distinct from that of all other countries. T h e following g e n e r a are found :—(Diplocentridae) Diplocentrus, two or three species, W e s t I n d i e s , B r a z i l ; (Ischnuridae) *Opisthacanthus one s p e c i e s , P a n a m a , C o l o m b i a ; (Iuridae) *Hadruroides, four or five species, W e s t Indies, P e r u , B o l i v i a ; *Caraboctonus, one species, C h i l i , B r a z i l ; (Chactidae) ^Broteas, four species, G u i a n a , B r a z i l , L a P l a t a ; *Megacormus, one species, M e x i c o ; Broteochactas, three species, G u i a n a , V e n e z u e l a , C o l o m b i a ; *Hadrurochactas, one species, B r i t i s h G u i a n a ; *Teuthraustes t w o species, E u c a d o r ; *Chactas a n d *Heterochactas, about t w e l v e species, V e n e z u e l a , C o l o m b i a , E c u a d o r , P e r u ; (Bothriuridae) *Bothriurus, six or eight s p e c i e s , P e r u , C h i l i , U r u g u a y , South B r a z i l ; *Brachistosternus, three or four species, P e r u , C h i l i , A r g e n t i n e ; '*Mecocentrus, one species, B r a z i l ; Phoniocercus, one species, B r a z i l ; *Thestylus, one s p e c i e s , B r a z i l ; *Centromachus, one species, Chili ; *Urophonius, t w o species, C h i l i , A r g e n t i n e , U r u g u a y ; (Buthidae) Centrums, m a n y species, W e s t Indies, C o l o m b i a , C h i l i ; *Heteroctenus, t w o species, H a y t i , M e x i c o , B r a z i l ; *Tityus, m a n y species, M e x i c o , W e s t Indies, C o l o m b i a , B r a z i l , A r g e n t i n e ; * A n a n t e r i s , one species, Brazil. T h e s e data show how v e r y specialised is the N e o t r o p i c a l fauna. T h e Chactidae are confined to the region, and, with the possible e x c e p tion of Cercophonius, none of the N e o t r o p i c a l genera of Bothriuridae are found e l s e w h e r e . M o r e o v e r , three out of the four g e n e r a of Buthidae are peculiar ; so, too, is the single genus of Ischnuridae, while the r e m a i n i n g genus of Buthidae occurs e l s e w h e r e only in the S o n o r a n P r o v i n c e of North A m e r i c a . N o t h i n g is k n o w n of the S c o r p i o n s of P a t a g o n i a . Darwin, h o w e v e r , tells us that they a r e found at least as far to the south as the 47th parallel. It is, of course, h i g h l y p r o b a b l e that the s p e c i e s of this country will prove to be n e a r l y related to those of the A r g e n t i n e R e p u b l i c . At present our limited k n o w l e d g e m a k e s it h a r d l y possible to

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divide the Neotropical R e g i o n into sub-regions. In a general w a y , h o w e v e r , the northern parts of the area seem to be characterised by the presence of Chactidae, and the southern by the presence of Bothriurida3 ; and it is interesting to note that both of these groups are absent from the W e s t I n d i e s . T h e r e are, too, some further points of interest connected with these i s l a n d s . F o r instance, the species known from the larger i s l a n d s — i . e . , C u b a , J a m a i c a , H a y t i , and P o r t o R i c o — a r e , for the most part, also found on the mainland of Central or S o u t h A m e r i c a ; w h i l e the species that h a v e been obtained in the smaller islands to the south-east—e.g., Montserrat, S t . L u c i a , S t . V i n c e n t , and G r e n a d a — a r e peculiar forms of the C e n t r a l and South A m e r i c a n genera Tityus and Diplocentrus.

S o m e of the facts connected with the distribution of S c o r p i o n s set forth in the preceding p a r a g r a p h s offer interesting points for further discussion. It is to be o b s e r v e d , in the first place, that a r m s of the sea constitute barriers which these a n i m a l s cannot p a s s ; yet, although their means of dispersal are v e r y limited, the antiquity of the group is so great that it has s u c c e e d e d in distributing itself o v e r all the contiguous land a r e a s of the g l o b e . In fact, as we h a v e seen, these a n i m a l s h a v e been met with in all parts of the continents which h a v e been e x p l o r e d , with the exception of the colder p a r t s of the Northern H e m i s p h e r e , and in all continental islands with the single exception o f N e w Z e a l a n d . B u t w e k n o w that i n p r e - G l a c i a l T e r tiary times they extended in E u r o p e as far to the north as w h a t is now the southern shore of the B a l t i c ; and there cannot be much doubt, one w o u l d think, that their a b s e n c e at the present d a y from all that area of the Northern H e m i s p h e r e which lies north of the 45th parallel of latitude is to be attributed to the recent glaciation of this part of the world. B u t their a b s e n c e from N e w Z e a l a n d is not to be so e a s i l y explained a w a y . It is clear, h o w e v e r , that we h a v e to account for the fact upon one of t w o h y p o t h e s e s , n a m e l y , that they h a v e never succeeded in r e a c h i n g the country in question, or that they h a v e been e x t e r m i n a t e d since a r r i v i n g there. T h e first hypothesis, h o w e v e r , seems h a r d l y likely to be the true one, if there has ever been an uninterrupted and long-continued landconnection between N e w Z e a l a n d and the south-eastern parts of A s i a by w a y of A u s t r a l i a or A u s t r o - M a l a y a . B u t if, on the other hand, the connecting land w a s composed m e r e l y of i s l a n d s , the intervening seas would probably h a v e afforded an effectual barrier to their migration. W i t h regard to the hypothesis of extermination, it m a y be said that, so far as is k n o w n , there is nothing in the p h y s i c a l conditions of N e w Z e a l a n d antagonistic to Scorpion life, and it must be left to the

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geologists to decide whether there is a n y e v i d e n c e in favour of the glaciation of this country w h i c h would account for the extermination of Scorpions, supposing they had e v e r succeeded in e s t a b l i s h i n g themselves there. F o r myself, I am disposed to think that none of the recent g r o u p s of S c o r p i o n s h a v e ever been represented in N e w Z e a l a n d ; in w h i c h case it s e e m s certain that the e x i s t i n g Scorpion population of A u s t r a l i a m a d e its w a y , like the M a m m a l i a , into the latter country after the isolation of N e w Z e a l a n d . S o , too, with M a d a g a s c a r . T h e a b s e n c e of nearly all the large E t h i o p i a n forms from this island s h o w s that the s e v e r a n c e from the mainland took place before the t y p i c a l African genera had appeared in the country. A n d the presence in M a d a g a s c a r of genera of Buthidae and Ischnuridae, peculiar but with m a r k e d A f r i c a n affinities, points to the conclusion that, at the time of the connection with A f r i c a , species of these t w o families were the principal if not the sole r e p r e s e n t a t i v e s of S c o r p i o n s in the E t h i o p i a n R e g i o n . A discussion of the fauna of M a d a g a s c a r n a t u r a l l y leads us to inquire whether a study of the distribution of S c o r p i o n s affords any support to the hypothesis of a former direct connection between this island and the Oriental R e g i o n . B u t since there is no s i m i l a r i t y between the species of the two a r e a s , we m a y dismiss the subject by s a y i n g that the S c o r p i o n s do not furnish a particle of evidence that the union has e v e r been more complete than it is at present. T h e a b s e n c e of evidence in favour of L e m u r i a obviously s u g g e s t s an e x a m i n a t i o n of the question of the e x i s t e n c e of A n t a r c t i c a , to which m a n y other groups bear w i t n e s s . B u t here a g a i n all the e v i d e n c e is on the n e g a t i v e side. F o r , firstly, there is the absence of S c o r p i o n s from N e w Z e a l a n d ; secondly, total d i s s i m i l a r i t y between the S c o r p i o n s of M a d a g a s c a r a n d A u s t r a l i a , and of S o u t h Africa and S o u t h A m e r i c a ; and, lastly, the almost complete w a n t of r e s e m b l a n c e between the Scorpions of A u s t r a l i a and those of S o u t h A m e r i c a . T h e one point of r e s e m b l a n c e between these t w o countries is the presence in A u s t r a l i a of a g e n u s of the Bothriuridae, a family which is almost exclus i v e l y confined to the N e o t r o p i c a l area. T h i s case has been cited by M r . F o r b e s , in his interesting p a p e r on the C h a t h a m I s l a n d s , as an item of e v i d e n c e in favour of A n t a r c t i c a . B u t , since furnishing M r . F o r b e s with the information that the A u s t r a l i a n Cercophonius squama occurs also in C h i l i , I h a v e found g r o u n d s for doubting the truth of the evidence upon which the information w a s b a s e d . If, h o w e v e r , it is so, the fact of its being the same s p e c i e s that occurs on these two shores of the S o u t h P a c i f i c favours the v i e w of artificial or fortuitous introduction ; for apart from this one there is not a single species or even g e n u s which is common to the Old and N e w W o r l d s . B u t whether or not the genus Cercophonius occurs in A u s t r a l i a and S o u t h A m e r i c a , we still h a v e to account for the presence in the former country of a Scorpion belonging to a family w h i c h is t y p i c a l l y S o u t h A m e r i c a n . It is possible, of course, that this m a y be e x p l a i n e d , as M r . F o r b e s

SCORPIONS.

supposed, on the hypothesis of a southern land-connection between the two countries. B u t this is not the only theory that will account for the c i r c u m s t a n c e ; for it is possible that the family to which the genera belong had once a wide extension in the Northern H e m i s p h e r e , and that although exterminated, for the most part, in the keener competition of more northern a r e a s , some of the g e n e r a , like the M a r s u p i a l M a m m a l s , h a v e found places of refuge in the countries to which they are now restricted ; and this supposition is borne out by the fact that a solitary representative of the family has been recently discovered in S u m a t r a . It is n e c e s s a r y to bear in mind that the g e n e r a l a b s e n c e of similarity between the Scorpions of the three southern extensions of land is not of the s a m e v a l u e in d i s p r o v i n g the former e x i s t e n c e of A n t a r c t i c a as is the absence of similarity between M a d a g a s c a r and the Oriental R e g i o n in d i s p r o v i n g the existence of L e m u r i a ; for while it is clear that the Scorpions could h a v e freely m i g r a t e d across a land lying in the centre of the tropical Indian O c e a n , it is equally clear that, unless there w a s a long-continued genial climate in the A n t a r c t i c S e a s , they could never h a v e succeeded in m a k i n g their w a y even along the northern coast-line of the southern continent that M r . F o r b e s has delineated. A further modification of S c l a t e r and W a l l a c e ' s Z o o - g e o g r a p h i c a l M a p that has been suggested, and often adopted, is the union of the so-called N e a r c t i c and Palaearctic into one region, for which the term H o l a r c t i c has been proposed ; but a study of the distribution of S c o r pions affords no support to this c h a n g e , i n a s m u c h as it s h o w s that none of the genera extend from one region to the other, a n d even when the families are taken into consideration, it is found that the similarity between the Palaearctic a n d N e a r c t i c is no greater than that between the Palaearctic a n d Oriental. T h e r e still remain one or two apparent anomalies in the distribution of some of the families of S c o r p i o n s to be accounted for. The first a n d strangest of these, furnished by the Ischnuridae, is the unquestionably close relationship that e x i s t s between the e x c l u s i v e l y S o u t h African genus Opisthocentrus and the genus Opisthacanthus, which is restricted to P a n a m a , C o l o m b i a , etc. A s o m e w h a t similar peculiarity is found in the c a s e of the two k n o w n genera of the Diplocentridae, n a m e l y , Diplocentrus, which is found in the Antilles and Central A m e r i c a , and Nebo, which occurs in A r a b i a , E g y p t , and S y r i a . A g a i n , coming further to the north, we find that in the Iuridae the L e v a n tine g e n u s Iurus has one of its nearest allies in the Californian Uroctonus, a n d that the Neotropical g r o u p of the Chactidae has a South E u r o p e a n representative in Euscorpius. T h e s e four c a s e s , taken together, seem to me to point to the conclusion that, at one period, these families h a d a w i d e l y - e x t e n d e d range in the N o r t h e r n H e m i s p h e r e , a n d w e r e enabled thereby to p a s s from E a s t e r n A s i a into W e s t e r n N o r t h A m e r i c a . A n d the one item of

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information we possess r e g a r d i n g c o m p a r a t i v e l y recent fossil S c o r pions is corroborative of this supposition. I refer to the c a s e of a S c o r p i o n described as a Tityus from the a m b e r beds of the B a l t i c . F r o m this we learn that, in p r e - M i o c e n e T e r t i a r y times, S c o r p i o n s in E u r o p e reached as far to the north as the 55th p a r a l l e l , that is, to about the s a m e latitude as the chain of islands w h i c h now connects K a m s c h a t k a with A l a s k a . M o r e o v e r , a l t h o u g h the generic determination of this S c o r p i o n cannot be u n r e s e r v e d l y a c c e p t e d , yet it is highly important to note that, at the present d a y , in the Old W o r l d the only S c o r p i o n s w h i c h could r e a s o n a b l y be identified as Tityus are found to the south of the tropic of C a n c e r . It s e e m s , therefore, legitimate to conclude that in p r e - G l a c i a l T e r t i a r y times the ancestors of our e x i s t i n g Old W o r l d tropical S c o r p i o n fauna e x t e n d e d far enough to the north in the E u r o p a e o - A s i a t i c continent to p a s s freely along any land-connection w i t h N o r t h A m e r i c a . B u t the a d v e n t of g l a c i a l conditions in later T e r t i a r y times, and the consequent extermination of the S c o r p i o n s in the northern parts of the N o r t h e r n H e m i s p h e r e , would soon put an end to the intercourse between the A s i a t i c and N o r t h A m e r i c a n species ; and these, under the c h a n g e d conditions, might h a v e become differentiated into the distinct t y p e s w h i c h inhabit these countries at the present d a y . T h i s supposition, then, of the former w i d e distribution in the Northern H e m i s p h e r e of the ancestors of the Ischnuridae and other tropical or s u b - t r o p i c a l families, furnishes, it seems to me, the most satisfactory e x p l a n a t i o n of the r e s e m b l a n c e s and differences that are o b s e r v a b l e between the S c o r p i o n s of the Old and N e w W o r l d s . M o r e o v e r , the restriction of the Diplocentridae and Ischnuridae at the present time in S o u t h A m e r i c a to the northern parts of this region points to relatively recent i m m i g r a t i o n of these g r o u p s from N o r t h America. In fact, it seems p r o b a b l e that they m a d e their w a y into the country at a t i m e when it w a s occupied by a n c e s t o r s of the e x i s t i n g N e o t r o p i c a l Bothriuridae a n d Buthidae ; a n d this last conclusion points to the further one that these latter t w o families belong to an older t y p e than the t w o before-mentioned g r o u p s , which are n e a r l y related to the Scorpionidae. T h i s hypothesis, too, is borne out by the confinement of the Bothriuridae in the E a s t e r n H e m i s p h e r e to S u m a t r a a n d A u s t r a l i a , and by the fact that, a l t h o u g h the Buthidae are cosmopolitan in their r a n g e , yet peculiar genera of the family are found i n S o u t h A f r i c a , M a d a g a s c a r , C e y l o n , A u s t r a l i a , and S o u t h America. R. I.

POCOCK.