i58 



Memoirs of the Indian Museum. 



[Vol.. V, 



genus. Hansen (1910 and 1912), who has in these publications instituted four new 

 species of Gastrosaccus , frequently remarks on the close similarity between the 

 females of the various species and the difficulty of separating them. As a result, 

 however, of his researches on the genus he came to the conclusion that the character 

 of the pleopods in the male afforded excellent specific characters and, following his 

 lead, I have used these characters to separate the new species here described. 

 The genus now comprises the following twelve species : — 



G. sanctus, van Beneden. G. bengalensis, Hansen. 



G. spinifer, Goes. G. pacificus, Hansen. 



G. normani, G. O. Sars. G. vulgaris, Nakazawa. 



G. erythraeus , Kossman. G. kojimaensis, Nakazawa. 



G. indicus, Hansen. G. muticus, sp. nov. 



G. parvus, Hansen. G. simulans, sp. nov. 



Of these twelve species, G. spinifer and the two species here instituted are imme- 

 diately distinguished by the possession of a fringe of spine-like filaments on the cen- 

 tral dorsal posterior margin of the carapace. The three species, G. spinifer , G. muticus 

 and G. simulans, may be distinguished among themselves by the character of the 

 exopod of the third pleopod of the male as shown in the text-figure and otherwise by 

 the following characters : — 





G. spinifer. 



G. muticus. 



G. simulans. 



Spine on fifth segment of the pleon. 



Present at all 

 sizes. 



Absent. 



Present in young, 

 absent in adult. 



Spines on the second joint of antennular pe- 

 duncle. 



3 



3 or 4 



4 



Spines on lateral margin of telson 



6-8 



14 



8-10 



Spines on inner margin of inner uropod 



9-11 



4 



4 



Size of adult specimens 



20 mm. 



6-7 mm. 



7-8 mm. 



The species of the genus Gastrosaccus may be arranged in two groups, according 

 to the structure of the pleopods of the male, as follows: — 



I. Endopod of the third pair, either rudimentary or a simple unjointed lobe. — 

 G. indicus, G. parvus, G. bengalensis, G. normani, G. pacificus, G. erythra- 

 eus. 



In this group the endopod, or both endopod and exopod of the second 

 pair of pleopods in the male, are not normal in shape and more or less 

 reduced. 



