DECAPODA. 43 



within their cavities, and whose claws, at least in the males, are 

 considerably thicker than the other feet. 



Mithrax, Leach. 



Robust claws: ends of the fingers like the bowl of a spoon; stem 

 of the lateral antennae sensibly shorter than the pedicle; the tail 

 composed of seven segments in both sexes. 



All the known species are from the American seas(l). 



Acanthonyx, Latr. 



A tooth or spiniform projection on the inferior side of the tibae; 

 under part of the tarsi pilose, and as if pectinated; superior surface 

 of the shell smooth. The tale of the males presents, at most, but 

 six complete segments(2). 



Pisa, Leach. 



Claws of a mean size, with pointed fingers; tibae without any spine 

 beneath, and the tail composed of seven segments in both sexes. 

 As in the preceding subgenera, the lateral antennae are inserted at 

 an equal distance from the fossulae that receive the intermediate 

 ones, and from the ocular cavities, or rather nearer to the latter. 



These, as in the genus Naxia, Leach, (3) have two ranges of den- 

 tations on the under part of the tarsi. Those have but a single row 

 of dentations, or a simple fringe of thick claviform cilia, under the 

 same joint. The latter constitute the genus Lissa of that author(4). 



Among those which have a range of dentations, the feet some- 

 times gradually diminish in length, as happens in his Pisa(5) pro- 

 perly so called, and at others, the third ones, in the males, become 

 abruptly shorter than those which precede them, as in his Chori- 

 nus(6). 



Pericera, Latr. 

 The Pericerae, though approaching the Pisae in the form and pro- 



(1) Mithrax spinicinctus, Latr.; Desmar., Consid., p. 150; Cancer kispidus, 

 Herbst., XVIII, 100; Cancer aculeatus, Herbst., XIX, 104; C. spinipes, ejusd., 

 XVII, 94. The lachus hircus, Fab., is perhaps a congener. 



(2) Maia glabra, Collect, du Mus. d'Hist. Nat.; Maia lunulata, Risso, I, 4; Li- 

 binia lunulata, Desmar. 



(3) Pisa aurita, Latr., Encyc. Method. P. monoceros, lb. 



(4) Pisa chiragra, Latr., Encyc. Method.; Desmar., Consid. 



(5) Pisaxyphias, Latr., lb.; ejusd., lb. P. aries,- P. barbicornis; P. corni- 

 gera; P. styx; P. bicornuta; P. trispinosa; P. armata, Leach, Malac. Brit., 

 XVII; Cancer muscosus ? , Lin.; P. tetraodon, Leach, lb. xx. 



(6) Pisa heros, Latr., Encyc. Method. 



