DECAPODA. 181 



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

 six complete segments*. 



Pisa, Leach. 



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

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

 As in the preceding subgenera, the lateral antennee 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 f, have two ranges of den- 

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

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

 same joint. The latter constitute the genus Lissa of that author +. 



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

 times gradually diminish in length, as happens in his Pisa%, pro- 

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

 abruptly shorter than those which j^rccede them, as in his Chori- 

 nus ||. 



Pericera, Latr. 



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

 portions of the claws, and the number of their caudal segments, are 

 removed from them, as well as from the other anterior subgenera, 

 l)y the insertion of their lateral antennae under the snout, and their 

 approximation to the fossulce lodging the intermediate ones, being 

 closer than to those which receive the ocular pedicles^. 



In the two following subgenera the ocular pedicles are short or 

 moderate, as well as in the preceding ones. But the claws, even 

 those of the males, are hardly thicker than the following feet. The 

 tail always consists of seven segments. In the 



Maia, Leach, 



The second joint of the lateral antennae seems to arise from the 

 internal canthus of the ocular fossee. The hand and the joint v.'hich 

 precedes it are nearly of the same length. The shell is ovoid. 



This subgenus established by Lamarck, and originally consisting 

 of a great number of species, comprises, at present, according to 

 the method of Dr. Leach, but one, the Cancer squinado, Herbst, XIV, 



* Maia glabra, Collect, du Mus. d'Hist. Nat. ; Maia lumdata, Risso, I, 4 ; 

 Lihinia htnulafa, Desmar. 



t Pisa aiirifa, Latr., Encyc. Method. — P. nionoceros, Ih. 



X Pisa chiragra, Latr., Encyc. Method. ; Desmar., Consid. 



§ Pisa xi/phias, Latr., lb.; — ejusd., lb. P. anes; — P. barbicornis ; — P. corni- 

 gera; — P. sfyx ; — P.bicvniuta; — P. frispinosa ; — P. arinata, Leach, Malac. Brit., 

 XVII; Cancer muscosus .' Lin.; — P. telraodon, Leach, lb. xx. 



II Pisa heros, Latr., Encyc. Method. 



5[ Maia favrus, Lam. ; Cancer cormtdo, Herbst., lix, 6. 



N.B. The genus Amathia of M. P. Roux, Hist, des Crust, de la Mediterr., &c., 

 liv. I, does not differ from my Pericera — it even appears to me to have the same 

 type. The Lithographic plates which accompany this work are distinctly and 

 faithfully executed. 



