244 Records of the Indian Museum. \\Oh. XIII, 



of additional species yet remain to be discovered on the Indian 

 coasts. 



I have included descriptions of two new forms obtained by 

 Dr. Annandale during his recent tour in the Far East. One of 

 these is from the Tai Hu in the Kiangsu province of China, a lake 

 which is fresh at all times of the year; the other was found in 

 brackish water in the Tale Sap in Lower Siam. 



We are at present very far from possessing a clear knowledge 

 of the species referred to this family. The descriptions and figures 

 of many of the older authors are a constant source of difficult^' 

 and the identity of numerous species described in the earlier half 

 of the nineteenth century still remains obscure. The confusion is 

 accentuated by differences of opinion regarding the genera. Many 

 authors appear to have distributed their species almost at random 

 and Haswell,' who places all the Australian forms in the genus 

 Hymenosoma, has expressed the opinion that '' the subdivision. . . . 



I'IG. I. — Hymenosoma oybiciilare, Desmare.sl. 

 Anterior part of carapace, seen from below. 



into the genera Hymenosoma , Hynienicus and Halicarcinus appears 

 to be unnecessary and based on extremely slight points of distinc- 

 tion." This view finds no support from subsequent writers, and it 

 is evident that its author was unaware of the characters of the 

 true Hymenosoma ; nevertheless, as explained below, I believe him 

 to have been right in uniting Hynienicus and Halicarcinus. 



The following notes on the genera are based on the material 

 in the Indian Museum, which contains in addition to twelve Indian 

 species, a number of specimens from China, Australia, New Zealand , 

 S. Africa and the Falkland Is., all the known genera with one 

 exception being represented. 



Hymenosoma was described by Desmarest in 1825,* the type 

 species being H. orhiculare from the Cape of Good Hope. It is one 

 of the most clearly defined of the genera comprised in the famil}^ 

 differring widely from all others in the complete absence of the 

 epistome (text-fig. i). The external maxillipedes almost encroach 



' Haswt'll, Cat. Australian Crust., p. 114 (1882). 



'^ Desmarest, Consid, gen. Crust., Paris, p. 163 (1825), 



