59 



the post-orbital crests are coarse and blunt without any distinct edge ; but in 

 other respects it agrees more nearly with P. tumidum and tiirgididimi. More 

 specimens are wanted in order to fix the position of the species. 



?^ Sikkira. J. Wood-Mason. 1 c? , 2 $ . 



10 



Subgenus III. : Geotelphusa, Stimpson. 

 Type : Geotelphusa dehaanii, Stimpson. ( SL^,^ i 7 



OeolelfiliHsa, Stimpson, Proc. Acad. Nat. Sci., Philad., x., 185S. 



GeoUlphmit (part), Mary J. Rathbun, Noiiv. Archiv. du Museum (4), VII., 1905. p. 200 {udi lit.). 



In Geotelphusa dehaanii, which is one of the two species upon which 

 Stimpson founded his genus Geotelphusa, the terminal joint of the mandibular 

 palp is simple, the 6th segment of the male abdomen is much broader than long, 

 and the exopodite of the external maxillipeds has a strong flagelluni. 



Stimpson's diagnosis is "Near Telphusa ; post-frontal crest obsolete, 

 antero- lateral margin entire." 



Among the species conforming to Stimpson's diagnosis there are : (1) some 

 —like '.' Potamon" Iwve—thai have the terminal joint of the mandibular palp 

 bifui'cate and the 6th segment of the male abdomen as long as its distal breadth ; 

 (2) others— like P. sikkimense—i\mX have the terminal joint of the mandibular 

 palp simple, the 6th segment of the male abdomen much broader than long, and 

 the exopodite of the external maxillipeds uon-flagellate ; and (3) others still — 

 like P. dehaanii — that have the tenniual Joint of the mandibular palp simple, the 

 (Hh segment of the male abdomen much broader than long, and the exopodite of the 

 external maxillipeds famished ivith the usual long flagellum. To these last it 

 seems well to restrict the name Geotelphusa. 



The Indian species referable to the subgenus Geotelphusa are three in 

 number, namely, P. (G.) enode, Kingsley, which is not represented in the collec- 

 tion ; P. (G.) adiatretum; and a small species, which I can not at present 

 characterize, very close to P. (G.) adiatretum. 



33. PoTAMON (Geotelphusa) adiatretum, Alcock. (Fig. 11.) 



Very near akin to Potamon {Geotelphusa) enode, Kingsley. 



Carapace : length about five-sevenths breadth, depth half length, smooth to 

 the naked eye, but under magnification finely pitted and with a few fine short 

 wrinkles near the lateral margin. Cervical groove present only as a crescent 

 defining the mesogastric area posteriorly. An extremely deep furrow separates 

 the epigastric crests. 



Front in adult less than a third the greatest breadth of the carapace ; it and 



