1900.] A. Alcock— Card nohgical Fauna of India. 305 



from Carcinoplax in having (1) a much shorter and broader carapace, 

 (2) a much shorter and broader buccal cavern, with external maxillipeds 

 that have the antero- external angle of the nierus remarkably produced 

 outwards, and (3) the 3rd to 5th abdominal terga of the male fused 

 together. From Gatoptrus it chiefly differs (1) in having the carapace 

 more subquadrilateral than elliptical, and (2) in the curious Amphitrite- 

 like form of the external maxillipeds. 



• Carapace deepish, subquadrilateral or subelliptical, vastly broader 

 than long, with little or no distinction of regions, convex fore and aft, 

 slightly so from side to side. 



The extent of the fron to- orbital border is vastly less than the 

 greatest breadth of the carapace, so that the anterolateral borders, 

 which may be toothed or entire, have a Cancroid-like curve. Front 

 square-cut and quite straight, not well separated from the supra-orbital 

 angles, slightly notched in the middle line, a third or less the greatest 

 breadth of the carapace. 



Orbits shallow, their upper border entire. The basal antenna-joint 

 is short, and the antennal nagellum stands loosely in the orbital hiatus. 

 The antennules fold transversely. 



Buccal cavern square-cut, much broader than long; the efferent 

 branchial canals of the palate very well defined. The merus of the 

 external maxillipeds is short and broad and has the external angle 

 much produced, as in many species of Neptunus. 



Chelipeds subequal, much more massive and longer than the legs ; 

 the hands however, which are somewhat tumid, are unequal in the adult. 



Legs slender, unarmed : in the Indian species the last pair are 

 almost as paddle-like as those of the typical swimming-crabs of the 

 Portunid family. 



Tn the male the abdomen covers the whole width of the sternum 

 between the last pair of legs, and the 3rd-5th abdominal terga are fused 

 together. 



The sternal canals of the male are more perfect than in any other 

 Gonaplacoid known to me. 



Key to the Indian species of Libystes. 



I. Antero-lateral borders of the carapace serrated almost 



exactly like those of Catoptrics nitidus L. EdivardsL 



II. Antero-lateral borders of the carapace entire ... ... L. Alphonsi. 



Distribution : Indo-Pacific (Madagascar to Sandwich Is.). 



