94 DR. J. G. DE MAN ON A NEW PEESHWATER [Feb. 19, 



coloured Kashmir race of the Asiatic Ibex inhabits the great 

 Snowy Eaoge of the Himalaya, where the snowfall is heaviest. 

 The darker Baltistan Ibex, on the other hand, is a dweller in a 

 district where the fall of snow is less ; while the Thian-Shan and 

 Siberian race, at least in part of its habitat, is found in arid 

 districts where the snowfall is still more limited. It would thus 

 seem probable that the type of coloration characteristic of each 

 of the four forms of the Asiatic Ibex mentioned above is directly 

 correlated with the environment of each particular race. 



3. Description of a new Freshwater Crustacean from the 

 Soudan • followed by some Remarks on an allied Species. 

 By Dr. J. G. de Man, of lerseke, Zealand, Holland. 



[Received January 21, 1901.] 

 (Plate X.) 



A male specimen of a Crab from the Bahr-el-Gebel, in the 

 Soudan, obtained by Capt. S. S. Flower, F.Z.S., in April 1900, has 

 been sent to me for examination. Though apparently belonging 

 to a species not yet described, it was, for the sake of certainty, sent 

 successively to Prof. Pfeffer at Hamburg and to Prof. Hilgendorf 

 at Berlin, who both informed me that in their opinion it repre- 

 sented a new species. I therefore venture now to describe it as 

 such. 



The carapace is very wide, the greatest breadth, just in the middle 

 between the post frontal crest and the transverse groove separating 

 the mesogastric and urogastric regions from one another, being 

 in proportion to the length as 5 : 3. The carapace is rather strongly 

 convex from before backwards, and somewhat convex transversely. 

 The prominent and sharp postfrontal crest extends to the antero- 

 lateral margins much as in Potamon {PotamoncmUs) auhryi 

 A. M.-E., a type specimen of which, a male from the Gaboon, 

 was kindly sent me by Prof. Bouvier. The postfrontal ridge is 

 interrupted by the mesogastric suture, that appears roof-like 

 (" dachformig," Hilgendorf, 'Die Land- und Siisswasser-Deka- 

 poden Ostafrikas,' 1898, p. 5). From this suture the crest 

 proceeds sinuously towards, but without uniting with, the lateral 

 margin of the cephalothorax, a narrow suture remaining between 

 the lateral margin and the lateral extremity of the crest, and this 

 lateral extremity for a very short distance curves backwards 

 (Plate X. fig. 3). In Potamon auhryi A. M.-E., on the contrary, the 

 postfrontal ridge unites with the lateral margin of the carapace. 

 When the cephalothorax is looked at from above, the postfrontal 

 crest appears quite smooth, only a few crenulations being observed 

 near the lateral exti-emities. In a front view (fig. 2) the free 

 edge of the ridge appears finely crenate, the crenulations slightly, 

 though rather irregularly, increasing in size towards the lateral 



