1896.] A. Alcock — Carcinological Fauna of India. 211 



The invagination seems to be chiefly due to the pushing up of the epimeral 

 margin against the resistance of the vault of the carapace — a pushing up which 

 may be inferred from the position of what remains of the " epimeral suture." 



The origin of the thoracic sinus from such a simple invagination is very appar- 

 ent in the isolated carapace of Leucosia unidentata. Here, viewed from the inside 

 of the carapace, the thoracic sinus is seen as the convexity of a pocket ; and, viewed 

 from the outside, the month of the sinus shows as a ring of large granules or 

 puckers resulting from invagination. 



Key to the Indian species of Leucosia. 



A. Normal genkra : free edge of front projecting beyond the 

 epistome : hands not foliaceous : — 



I. Carapace conspicuously longer than broad, bluntly 

 rhomboidal, quite devoid of definite pubescence, the 

 thickened epimeral edge never visible in all its extent, 

 dorsally, when the carapace is held, without any inclin- 

 ation, straight in front of the observer's eyes : front 

 never ending in three sharp horizontal prongs: the 

 thoracic sinus always defined in some part of its extent 

 by large granules visible to the naked eye : no extensive 

 growth of hair, or definite patches of spongy pubes- 

 cence at the base of the upper surface of the arm : 

 meropodites of legs snbcylindrical : abdomen in both 

 sexes consisting of 4 pieces : — 



1. Outer edge of hand never carinate : front dorsally 

 convex in all its extent : posterior margin of carapace, 

 in the adult, usually gently convex, with its external 

 angles not defined : — 



i. True postero-lateral margin of carapace beaded 

 as far as the level of the base of the last pair of legs : 

 ventral surface of ischium of external maxillipeds of 

 female almost flat — never broadly carinate : — 



a. A loop of large granules between the base of the 

 chelipeds and the margin of the carapace : two 

 small red and white ocelli on either side of the 



gastric region L. unidentata. 



h. A single row of large granules between the base 

 of the chelipeds and the margin of the carapace, 

 and above it a second row of very small granules 

 running into the puckered edge of an almost cir- 

 cular bight in the pterygostomian region : no ocelli Z. ohtusifrons. 

 ii. True postero-lateral margin of carapace beaded 

 only up to the level of the base of the first pair of true 

 legs : a single row of large granules between the base 

 of the chelipeds and the margin of the carapace : — 

 a. Carapace, excluding the whole front, broader 

 than long, its posterior margin gently convex : — 

 aa. Thoracic sinus deep, the convex edge of the 

 ptei'ygostomian region, which defines the siuua 



