70. 



Subfamily 2.— GECARCINUCIN^. 



Genus II. — Paratelphusa, Edw. 

 Type : Paratelphusa tridentata, Edw. 



Paratelplmsa, Milne Edwards, Ann. Sci. Nat. Zool. (3), XX., 18,i.3, p. 213. 



The genus Paratelphusa differs from the genus Potamon only in the follow- 

 ing particulars : — 



(1) It is unusual for the abdomen of the adult male to be regularly 

 triangular ; it is far more usual for its distal half to be narrowed, the narrow- 

 ing beginning suddenly at the 5th or 6th segment. Whether this contraction 

 is marked or not, the 6th segment is never broad, its length almost always 

 being equal to, and not unseldom exceeding, its distal breadth ; and the 7th 

 segment is never broadly triangular, but is narrowly semi-elliptical, or tongue- 

 shaped, or at least elongate. 



(2) The mandibular palp is of a peculiar pattern ; the first two joints are 

 not separately distinguishable — they certainly have no movement independent 

 of one another ; and the terminal joint is divided from the base into two lobes 

 — a dorsal and a ventral. The dorsal lobe, which, in repose, lies behind the 

 incisor process of the mandible, is falciform and corresponds with the entire 

 terminal joint of Potamon. The ventral lobe, which, in repose, overlaps the 

 incisor process of the mandible, is a broad oval plate, and corresponds with a 

 tuft of hairs that sometimes occurs in Potamon. 



(3) It is not uncommon, though not by any means the rule, for the edges 

 of the ineropodites of the external maxiUipeds to fall conspicuously short of 

 the edge of the epistome, so as sometimes even to leave the siphon-plate of the 

 endopodite of the 1st maxillipeds slightly exposed : this is a step towards the 

 condition of the parts in Gemrcinucus. 



(4) It is unusual for any distinct gap to exist between the lower border 

 and the outer-upper angle of the orbit. 



It is impossible from the literatiu"e alone to determine the incidence of this 

 genus. As regards Indian species, all that can be said is that the genus, as 

 here defined, includes, inter alia, a selection from the subgenera Potamon, 

 Potamonautes, Geotelphusa, and Paratelphusa of Miss Rathbun's great mono- 

 graph. The type of the genus is Paratelphusa tridentata, Edw. 



The Indian species of this large genus may be arranged in six groups, to 

 which, perhaps, the name of .subgenera may be attached. A seventh section 

 is not a subgenus, but includes aberrant members of two of the other groups 



