82 Records of the Indian Museum. [Vol. X, 



tion. which is also found in the genus Alope, has been discussed at 

 length by Coutiere ; he considers it to be a case of ' dimorphism ' , 

 but his application of the term to the phenomena found in these 

 genera is open to question. 



In Thor, on the other hand, it is the third peraeopods which 

 are affected. In males of this genus the third leg is proportionately 

 much longer than in the female and bears a different type of 

 spinulation. 



If my results be accepted, the sexual modifications in one 

 species of Latreutes (L. mucronatus) are of a very far-reaching 

 nature, the whole form of the animal being different, while dis- 

 tinctions of the most striking character are found in the form of 

 the rostrum. 



The normal variation found in the species of certain genera is 

 astonishingly great, especially as regards the form and armature 

 of the rostrum, and it is unfortunate that almost implicit reliance 

 was placed on this character by many of the older authors. As a 

 consequence, a ver}^ large number of species stand in need of re- 

 definition and considerable difficulties have been met with in 

 identification, more particularly in the genera Latreutes and 

 Hippolysmata. 



In examining the Indian forms I have described three new 

 species and one variety, while two fresh genera are proposed, both 

 based on forms already described. Out of a total of twent3'-two 

 genera, the number now known from the Indo-pacific region' is 

 fifteen, of which twelve have been found on the coasts of British 

 India. 



A sound basis for the classification of the genera was outlined 

 by Caiman in igo6* on characters derived from the branchial 

 formula and the development of the mandible. The Indo-pacific 

 genera may be distinguished by the use of the following key, which 

 is adapted and expanded from that given by Caiman, The 

 genera Ogyris, Stimpson, and Pterocaris, Heller, are regarded as 

 members of the Alpheidae and are not included therein. I have 

 not seen examples of the genera Nauticaris , Ligur and Mimocaris. 



Key to the Indo-Pacific genera of Hippolytidae. 



A. Arthrobranchiae present at base of first four pairs of peraeo- 

 pods [mandible with three-segmented palp ; many seg- 

 ments in carpus of second peraeopods]. 



I A movable tooth at base of uropods. 



A. Mandible with incisor-process ... ... Savon. 



B. Mandible without incisor- process ... ...Nauticaris. 



II. No movable tooth at base of uropods. 



A. Mandible with incisor-process ; last three peraeopods 



not abnormally slender ... ... ... Merhippolyte. 



' Under this term I include the area extending from the Red Sea and Delagoa 

 Bay to New Zealand, Oceania, the Hawaiian Is. and japan. 

 2 Caiman, Ann. Mag. Nat. Hist. (7), XVH, p. 29. 



