Carcinological Fauna of India. 305 



from Carcinoplax in having (I) a raucli shorter and broader carapace, 

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

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

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

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

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

 like form of the external maxillipeds. 



Caraisace 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 fronto-orbital border is vastly less than the 

 greatest breadth of the carapace, so that the autero-laferal bor-ders, 

 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-joiufc 

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

 The antennules fold transversely. 



Buccal cavei'n square-cut, much broader than long ; the etfereut 

 branchial canals of the palate very v.ell defined. The merus of the 

 external maxillipeds is short and broad and has the external angle 

 much produced, as in many species of Neptuniis. 



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

 the hands how^ever, which are somewhat tumid, are unequal in the adult. 



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

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

 Portunid family. 



In the male tlie abdomen covers the whole width of the sternum 

 between the last pair of legs, and the ord-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. 



1. Antero-lateral borders of the carapace serrated almoBb 



exactly like those of Cafo^jtras wifidus L. Edwardsi. 



II. Antero-lateral borders of the carapace entii-e ... "... L. Alphongi- 



Didrihiilkm : Indo-Paoific (Madagascar to Sandwich Is.). 



647 



