Carcinologieal 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 Lencoma 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 genera : free edge of front projecting beyond the 

 epistome: hands not foliaceous : — 



I. Carapace conspicuously longer than broad, bluntly 

 x-homboidal, 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 subcylindrical : 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 fiat — 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. 



b. 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 L. obtutifrons. 



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 



pterygostomian region, which defines the sinu* 



216 



