Carcinological Fauna of India. 227 



The thoracic sinus is a deep obscurely Y-shaped cavity full of hair, 

 the tail of the Y being defined by a row of 5 flat pearly granules situated 

 above the chelipeds, the inner limb of the Y being very short, and the 

 outer limb of the Y being produced up to the antero-lateral border to 

 accent the boundary between the hepatic and branchial regions, the 

 concavity of the fork of the Y being sharply defined by the smooth con- 

 vex edge of the pterygostomian region. 



The front is broader than long, deflexecl and obscurely bilobed at 

 tip, and a little concave in the mid-dorsal line anteriorly. 



The ventral surface of the ischium of the external maxillipeds of the 

 female is perfectly flat. 



The edges of the trigonal arm are tuberculate : on the upper sur- 

 face of the arm two short rows of tubercles arise from a mass of 

 granules and short hairs at the base of the arm, and run, one towards 

 the inner, one to the outer, edge of the arm : the wrist and the hand 

 are quite devoid of granules : the fingers are nearly as long as the hand, 

 and meet only at the tips. 



The legs have all the joints compressed but not dilated. 



The abdomen of the male consists of 4 pieces, that of the female 

 of 3 pieces only. 



Colours in spirit : yellowish white with yellowish brown markings, 

 the hand and the fingers each with a brownish cross-band, the abdomen 

 of the female with brownish yellow markings in its anterior (true 

 posterior) third. 



A male and an egg-laden female from the Nicobars : the carapace 

 of the male is 11 millim. long and 10 millim. broad, that of the female 

 is 12 xll"5 millim. 



57. Leucosia sima, n. sp. Plate VI. fig. 5. 



Very closely related to L. cumingii, but differs from it, and from 

 all other species of the genus, in the length of the posterior margin of 

 the carapace, which is considerably more than half the greatest breadth 

 of the caiapace. Its form therefore would be broadly hexagonal, but 

 owing to the shortness of the front and to the great convexity of the 

 hepatic regions, it almost forms a pentagon. 



Besides in the form of the carapace, which is unique in the genus, 

 it differs from L. cumingii, Bell, only in the following characters, adult 

 females being compared : — ■ 



1. The front hardly breaks beyond the general convexity of the 

 anterior half of the carapace owing to the still greater angular promi- 

 nence of the hepatic regions. 



2. The antero-lateral margin of the carapace behind the angular 



232 



