138 Records of the Indian Museiim. [Vol. XIX, 



In both these features the family differs from the Atyidae and 

 Hoplophoridae and resembles more speciahzed forms which do not 

 possess exopods. 



The families of Caridea in which exopods exist on two or more 

 pairs of peraeopods do not, for the most part, show any very close 

 agreement with one another in other respects, and this fact points 

 to the conclusion that exopods persisted among ancestral forms 

 while considerable modifications in other directions were effected. 



The possibility that exopods in some instances may actually 

 have reappeared cannot be dismissed as altogether improbable. 

 They are of frequent occurrence in the larvae of Caridean families 

 that do not posses them when adult, and it is not difficult to 

 imagine that their occasional reappearance might be caused by 

 a persistence of larval characters into the adult stage. 



The presence of a series of exopods on the legs is thus by 

 itself insuificient to determine true relationship among the Caridea 

 and it appears probable that better indications of affinity are 

 afforded b}' the structure of the mouth-parts, especially of the 

 mandible and maxilla. In the latter characters Discias shows 

 a marked resemblance to the Hippolytidae and Palaemonidae 

 and, notwithstanding the differences in the first two pairs of peraeo- 

 pods, it is in these families, I believe, that the Disciadidae find 

 their nearest surviving allies. Discias is without doubt the most 

 specialized Caridean genus that possesses a full series of exopods. 



The species obtained in the Andamans is distinguished 

 from that found in the Galapagos Is. b}- characters which are 

 clearl}' not more than specific. Miss Rathbun's specimens were 

 all females; in the collection from the Andamans both males and 

 females occur, the former differing from the latter only in the 

 normal modifications of the first two pairs of pleopods. 



The specimens were all found together on a yellow sponge. 

 In the absence of precise field observations it is not possible to 

 say whether the association was fortuitous or whether the prawn 

 and sponge are synoecious, though the remarkable chelae of the 

 prawn suggest that it must have some peculiar mode of life. 



Family DISCIADIDAE. 



1902. Discidae, Rathbun, Proc. Washington Acad. Sci., IV. p. 289. 



Genus Discias, Rathbun. 



1902. Discias, Rathbun, I.e., p. 290. 



Discias exult sp. nov. 



Plate VIII. 



In general appearance the species bears some resemblance 

 to small Pasiphaeids belonging to the genus Leptochela, but is 

 immediately distinguished by the remarkable character of the 

 first two pairs of legs. 



