1918.] Stanley Kemp: Dccapoda of the InJe Lal<e. 



87 



to contain short stiff bristles, but these are completely worn away in 

 the majority of the specimens. 



The second pair of walkin<>' legs is a little less than twice the length 

 of the carapace. The jjropodites show only indistinct traces of the 

 double anterior margin found in P. andersonianum and other species ; 

 those of the penultimate pair vary from 2.^ to about 2| times as long as 

 broad. The posterior margin of each propodus is armed with from two 

 to four spinules and ends in a sharp spine. 



Fig. 2. — Potninon (Potamon) actnithicum, sp. nov, 

 rt, b. Outline of left .side of carapace. 



c. Third inaxillipede. 



d. Chela of old female. 



e. Abdomen of male. 



In a male (not perhaps fully adult) the sixth abdominal somite is 

 half as long as broad at the base, while the seventh, which is triangular 

 is a little broader than long (text-fig. 2c). 



The measurements (in nun.) of the carapace in eight specimens are 



as follows : — 



Sex 



Length 

 Breadth 

 Depth 



Potamon acanthicum may be distinguished at a glance fi'om all other 

 Indian Potamonidae by the character of the antero-lateral border of the 

 carapace. The sharp isolated spines with which the anterior part of this 

 border is provided apjiear to be an extreme modification of the serrate 

 or cremdate margin seen in most s})ecies of the sul)genus Potamon ; they 

 differ widely in character from the large flat teeth found in Indian 

 species of Acanthotelphai^a. In Potamon niJoficuin,''- however, the type 

 species of the subgenus Jcan/hotelphusa (and in a few other species all 

 found in Africa or Madagascar) the teeth are small, conical and irregular, 



1 Potninon {Paratdphiimi) niloticiis (M.-Ed\v.), Rathbuii, Xoar. Arch. Mus. Purin 

 (4), VII, p. 26 3, pi. xii, fig. 15 (HJ05). 



