1 IG MR. R. 1. pococK ON THE SCORPIONS [Mar. 18, 



the tibiae of the two posterior legs were armed with a spur ; the 

 pectiiial teeth were all alike ; the stigmata were slit-like. 



This diagnosis agrees more nearly with the plan of Isometrus 

 than with that of any other genus, notwithstanding that there 

 is in Isometrus a single lower tooth on the immovable digit of the 

 cheliceia?. Isometrus is cosmopolitan, and in Australia, Africa, and 

 America it appears to have given rise to three distinct genera. In 

 Australia Isometroides has sprung up through the loss of the spine 

 beneath the aculeus and by the acquisition of coarse punctulation on 

 the under surface of the fifth caudal segment ; in America Centrums 

 originated by the development of short rows of teeth connecting the 

 extieniities of the median rows of the digits of the chelae ; in Africa 

 Buthus arose when a second inferior tootli appeared behind tlie first 

 on the immovable digit of the chelicerse. Beyond this stage RJtoptru- 

 rus has not j)assed ; but Grosplius has lost a distinct spine beneath the 

 aculeus, and in the female the basal pectinal tooth has become dilated. 

 Paralnitlms can be derived from Grosplius by a sHght modification in 

 the arrangement of the denticles on the chelae, by the loss of the 

 enlarged pectinal tooth (perhaps through its fusion with the shaft of 

 the pecten), and by an increase in the strength of the tail ; whether 

 Bvthvs (s. s.) has been derived by the development of lateral tergal 

 keels from Parabutlms or Grosplius it is not easy to say ; but that 

 Prionurus has been developed from Buthus by an alteration in the 

 form of the tail will probably not be disputed. 



Lepreus resembles Grosplius in possessing an enlarged basal pec- 

 tinal tooth in the female ; but whether this genus has been derived 

 from Grosplius by the loss of the two lower teeth, and by a modifi- 

 cation in the armature of the chelae, cannot as yet be settled. But 

 inasmuch as tlic arrangement of the denticles on the chelae more 

 nearly approaches in Lepreus than it does in Uroplectes what is met 

 with in Grospjlius or Isometrus, I consider that Uroplectes is a 

 descendant of Lepi-eus. 



Butheolus is isolated, and may have been derived from either 

 Buthus or Isometrus. 



liefore proceeding to a consideration of the genera, it will be well 

 to discuss shortly the armature of the digits of the chelae and the 

 probable origin of the various modifications that are presented. 



Generally sjieaking, the dentition throughout the family may be 

 described as consisting of a number of oblique, overlapping, parallel 

 rows of fine close-set denticles. On each side of this median series 

 there is a row of larger, more widely separated teeth, and the ques- 

 tion to be decided in connection with these lateral teeth is whether 

 thev have heen derived from the median rows or liave arisen indepen- 

 dently of them. However, after examining many genera and species 

 of Scorpionidfe as well as of Butliidce I am strongly inclined to 

 believe that the lateral teeth have been derived from the median 

 seiies, and that originally the armature of the chelte consisted solely 

 of a number of oblique, overlapping, parallel rows of close-set den- 

 ticles, and that perhaps one or two terminal denticles of each row were 

 larger than the rest. From this relatively simple disposition of 



