56 



Subgenus II. : Potamiscus, Alcock. 



Type : Potamiscus annandalii. 



In this group or subgenus the exopodite of the external maxillipeds is 

 either non-flagellate or carries only a papillar vestige of a flagellum. 

 The species may be tabulated as follows : — 



1. Epigastric crests distinct; post-orbital crests merged in the rugosities of 



the carapace ; cervical groove quite indistinct antei'iorly . . P. sikkimense. 



2. Epigastric crests distinct ; post-orbital crests very bi-oad and blunt, but 



quite distinct ; cervical groove distinct in all its course . . .P. tuiinduliim. 



3. Epigastric crests distinct, not or hardly separated from the almost 



trenchant post-orbital crests ; cervical groove indistinct anteriorly . P. annandalii. 



30. PoTAMON (Potamiscus) sikkimense, Rathbun. (Fig. 48.) 



Potamou [Geotelphusa) sikkimeuxis. Mary J. Rathbun, Nouv. Archiv. du Museum, Paris (4), VII.. 1905, p. 219, 

 vi., pi. xviii., fig. 7. 



Carapace : length slightly exceeds three-fouiths breadth, depth equals 

 half length ; decidedly convex fore and aft ; its surface abundantly pocked ; 

 the frontal, post-frontal, post-orbital, and antero- lateral regions rugose ; the 

 side-walls with fine oblique striae, which also pass across the postero- 

 lateral borders. 



Only that part of the cervical groove which delimits the mesogastric 

 area is deep-graven, the rest of the groove delimiting the gastric region 

 from the epibranchial regions being a faint shallow deiDression. The fore-lobe 

 of the mesogastric areola is well defined, the median groove being prolonged 

 almost to the edge of the front. 



Epigastric crests bluntly tumid, rugose ; post- orbital crests somewhat 

 confused with the rugosities of the carapace. 



Front one-third the greatest breadth of the carapace, declivous, square-cut, 

 but with the angles rounded, very faintly bilobed in a dor.sal view only. 



The lower border of the orbit runs into the upper border, without gap or 

 tooth, or only a small tooth. 



Antero-lateral borders of carapace well defined, irregularly crenulate ; the 

 position of the very small epibranchial tooth is chiefly marked by a small break. 



In the adult male abdomen the 6th segment is nearly twice as broad as 

 long, and the 7th segment is as long as broad. 



Mandibular palp simple. ExojDodite of external maxillipeds non- 

 flagellate ; the meropodite of these appendages about as long as broad. 



Chelipeds a little unequal in the male, almost equal in the adult female ; 

 their extensor surface squami-rugose ; spine at inner angle of carpus coarse 



