316 Mr. R. I. Pocock on new Genera 



Family Scorpionidse, 



Subfamily Ischnurini. 



Opisthocentrus, gen. nov. 

 (PL XIV. figs. 2 and 3.) 



Differs from Opisthacanthus, Peters, of which elatus, Ger- 

 vais, is the type, in that the anterior border of the carapace is 

 less deeply excised, the lateral eyes less prominent and eitlier 

 subequally spaced or with the distance between the posterior 

 and median greater than that between the median and anterior, 

 in having only a small projection on the anterior aspect of the 

 brachium, in having the genital operculum very much smaller, 

 being shorter, in fact, than the side of the sternum, and much 

 wider than long, in having the pectines narrower at the base, 

 and the tactile area of the teeth limited to the posterior distal 

 extremities of these organs. 



Type, 0. afn'canus (Simon). 



I establish this genus for those species of Opisthacanthus 

 that have been described from Africa. So far as my exami- 

 nation extends these African species differ in a number of 

 characters from the South American form Opistliacanihus 

 elatus. It may be that these characters are of small value in 

 themselves, and it would be bold to assert that every one of 

 tiiem is of itself of generic importance. But the aggregate 

 value of them all, coupled with the wide difference in the 

 geographical distribution of the two types, is sufficient, I 

 think, to justify the adoption of the view of their importance 

 that is here put forward. 



In Opisthacanthus elatus the carapace is deeply excised in 

 the middle line, the lateral eyes are prominent, the space be- 

 tween the anterior and median being greater than that be- 

 tween the median and posterior; there is a large dentiform 

 prominence upon the brachium as in Ischnurus and Hormurus ; 

 the genital operculum is large, being nearly as long as wide, 

 and longer than the side of the sternum, in the female it is 

 heart-shaped, being noticeably produced posteriorly ; the 

 pectines are generally very wide at the base, owing to the 

 size of the basal intermediate lamella, and the teeth appear 

 to have been rotated so that the tactile areas which generally 

 look distally and externally are entirely external and extend 

 over nearly the whole of the exposed surface of the organ (at 

 least in the male). 



