116 MR. R. I. 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 sHt-like. 



Tliis diagnosis agrees more nearly with the plan of Isorr.etrus 

 than with that of any other genus, notwithstanding that there 

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

 chelicerse. Isometrus is cosmopolitan, and in Australia, Africa, and 

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

 Australia Tsometroides has sprung up through the loss of the spine 

 beneath the aculeus and by the acquisition of coarse punctulation on 

 the under surface of tlie fifth caudal segment ; in America Centnirus 

 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 tooth appeared behind the first 

 ori the immovable digit of the chehcerse. Beyond this stage Rhoptru- 

 rus has not ])assed ; but Grosplms has lost a distinct spine beneath the 

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

 Parahutlius can be derived from Grosphushy a slight modification in 

 the arrangement of tlie denticles on the cbelse, 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 

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

 keels from Parabuthus or Grospltus it is not easy to say : but that 

 Prionnrus has been developed from Buthus by an alteration in the 

 form of the tail will probably not be disputed. 



Lepreus resembles GrospJius 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 oi the chelse, cannot as yet be settled. But 

 inasmuch as the 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 Lepreus. 



Butheolus is isolated, and may have been derived from either 

 Buthus or Lsometrus. 



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

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

 ])robable origin of the various modifications that are presented. 



Generally sjieaking, the dentition throughout the family may be 

 described as consisting of a number of obhque, 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 been derived from the median rows or have arisen indepen- 

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

 of Scorpionidce as well as of Buthidce I am strongly inclined to 

 believe that the lateral teeth have been derived from the median 

 series, and that originally the armature of the chelae 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 



