234 'Dr. W. T. Caiman on a new 



XXV. — A new River-crab from (lie Transvaal. 

 By W. T. Calman, D.Sc. 



(Published by permission of tbe Trustees of the British Museum.) 



A RIVER-CRAB recently sent for determination by Dr. E. 

 Warren, of the Natal Museum, Pietermaritzburg, appears to 

 be sufficiently interesting to merit brief description. 



Potamon (Potamonautes) warreni, sp. n. 



Description. — Resembling very closely P. perlatnm (Milne- 

 Edwards), but having the antero-lateral margin of the cara- 

 pace armed with a series of about eight curved spiniform 

 teeth. The first tooth stands at the end of the postfrontal 

 ridge ; the following teeth diminish in size (not quite regu- 

 larly) from before backwards, passing into a line of granules 

 that curves on to the dorsal surface. The surface of the cara- 

 pace and limbs is rather smoother than in most specimens of 

 P. perlatum, the postfrontal ridge, the margin of the front, 

 and the upper margin of the orbit are nearly smooth, but the 

 lower margin of the orbit is rather strongly toothed. 



Measurements. — 



mm. 



Length of carapace 50 



Greatest breadth of carapace 70 



"Width of front between orbits 23"5 



Walking-leg of second pair (not fully extended) . . 85 

 Meropodite of second walking-leg 30 X 11 



Occurrence. — " Potchefstroom, Dr. Cawston, December 

 1917." 1 ? carrying young (holotype). Brit. Mus. 



Remarks. — It is possible that the specimen described above 

 may only deserve to rank as a varietal form of P. perlatum, 

 since it appears to differ from typical specimens of that species 

 only in the armature of the antero-lateral margins of the 

 carapace. This character, however, is so conspicuous, and 

 has been accorded such importance in the classification of the 

 family, that it seems advisable to call attention to it by a 

 specific name. 



I have examined, for the purpose of comparison, a con- 

 siderable series of P. perlatum from various localities in 

 South Africa, and in all the specimens the antero-lateral 

 margins are either finely granular or minutely denticulate, 

 the granules or denticles being not only very much smaller 

 but also much more numerous than the conspicuous teeth of 



