CarcincSog'eal Fauna of India. 263 



the surface, usually, crisply granular, spiny, or tubercular, but some- 

 times almost smooth to the naked eye. 



Front bilobed and prominent, or if not prominent then distinctly 

 pinched off from the gastric and hepatic regions. 



Orbits with three sutures in the upper and outer wall, with a cleft 

 in the inner wall, and usually with the inner canthus prolonged into a 

 spine : eyes small. 



The antennules fold very obliquely. The antennae are small, and 

 their basal joint loosely fills the cleft, in the inner wall of the orbit. 



The buccal cavern is elongate-triangular : the external maxillipeds 

 have the ischium from 2f to 3 times the length of the bluntly-triangular 

 merus : their exognath is narrow, with the outer border nearly straight. 



The chelipeds are very slender and are usually about twice the 

 length of the carapace — either a little more or a little less ; their joints 

 are cylindrical, the palm alone being a little swollen at base : the fingers 

 are long and very slender, their opposed edges being finely ctenoid, 

 with larger denticles at long intervals ; they open in a nearly vertical plane. 



The legs are slender. 



The abdomen of the male usually consists of 5 pieces, that of the 

 female of 4 or 5. 



Key to the Indian species of Arcania. 



I. Margins of the carapace with spines, 

 hepatic regions dorsally convex : abdomen 

 of adult male consisting of 5 pieces : — 

 1. Fingers longer than the hand : 

 surface of carapace either smooth 

 (microscopically granular), or with 

 small granules all of one size : — 

 i. Lateral median epibranchial 

 spines nearly straight, far 

 longer than any of the other 

 spines, their length often be- 

 ing equal to the breadth of 

 the carapace : — 



a. Seven spines on margins 

 of carapace, — 3 very 



large, 4 smaller A. septemspinosa, 



(Fabr.) 



b. Five spines on margins 

 of carapace, — 3 very 



large, 2 smaller A. quinquespinosa. 



268 



