44 



groove at the usual point, outside which they are low and quite confused with 

 the wrinkles of the carapace. 



In the male abdomen the 6th segment is nearly twice as broad as long, and 

 the 7th is nearly as long as broad. 



Palp of mandibles simple. Merus of external maxillipeds nearly as long 

 as broad ; the exopodite of these appendages with only a vestige of a flagellum. 



Chelipeds a little unequal, the extensor surface pitted and uneven rather 

 than rugulose ; spine at inner angle of carpus coarse but shai'p ; fingers as long 

 as palm, fluted and pitted. Legs (1st and 2nd pairs) about as long as chelipeds ; 

 dactyli longer than propodites ; propodites not twice as long as broad. 



Carapace of an adult female |ths inch long, just over 1 inch broad, 

 ruths inch deep. 



— — -. Sikkim. J. Wood -Mason. 1 cj, 2 ? (types of the species). 



Group IV. : austenianwn group. 



As in Groups I., II., and III., the cervical groove cuts the post-orbital 

 crests at a point in the longitude of the inner angle of the external orbital 

 tooth, and as in Group II. the merus of the external maxillipeds is as long as 

 broad. Though the carapace as a whole is flat behind the frontal slope, the 

 anterior part of the ejiibranchial regions is distinctly convex. But the 

 characteristic feature in this group are the long slender legs, the propodites of 

 the two middle pairs being three or four times as long as broad. 



1. Aveolation of carapace distinct; breadth of front, in adult, more than 



a fourth the greatest breadth of the carapace . . . .P. cmstenianum. 



2. Areolation of carapace indistinct; front, in adult, less than a fourth 



the greatest breadth of the carapace . . . . .P. simulum. 



23. Potamon {Potamoti) cmstenianum, Wood-Mason. 



Telphusa austeniana, Wood-Mason, Journal Asiatic Society of Bengal, XL., part II., 1871, p. 203, pi. xiii. 

 Potamon austenianus, Mary J. Rathbun, Nouv. Archiv. du Museum, Paris (4), VI., 1904, p. 287 {wbi lit.). 



There is no specimen of this species in the collection. The species, which 

 is found at Cherra Punji, differs from all its congeners except P. simulum in the 

 enormous length of the legs. The characters which distinguish it from P. 

 simulum are given in detail with the description of the latter species. 



24. Potamon (Potamon) simulum, Alcock. (Fig. 7.) 



This species is distinguishable from all its fellows of the subgenus, except 

 P. mistenianum, by the long slender legs. 



It seems to differ from P. austenianum in the following particulars :■ — 

 (1) The carapace is shorter and wider ; 



