DECAI’ODA. 
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 ; tibim 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 oevdar 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 row 
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- 
])erly so called, and at others, the third ones, in the males, become 
abruptly shorter than those which precede them, as in his Chori- 
IlllS ||. 
PiiRiCKRA, Latr. 
The Pericerae, though approaching the Pisoe 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, 
by the insertion of their lateral antennse under the snout, and their 
approximation to the fossulae lodging the intermediate ones, being 
closer than to those which receive the ocidar pedicles^. 
In the two following sidigenera 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 fossae. The hand and the joint which 
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 jiresent, according to 
the method of Dr. Leach, but one, the Cancer squinado, Herbst, XIV, 
* Maia ylabra, Collect, du Mus. d’Hist. Nat. ; Maia Innulata, Risso, I, 4 ; 
Libiniu lunulata, Desmar. 
t Pisa aiirila, Latr., Encyc. Method. — P. nwnoccros, Ih. 
:J; Pisa chiraya, Latr., Encyc. Method. ; Desmar., Cousid. 
§ Pisa xijphias, Latr., Ib. ; — ejusd., Ib. P. uries\ — P. barbiconiis ; — P. corni- 
gera; — P. styx ; — P. bicornida; — P. frisjniwsa ; — P. aniiafa, Leach, Malac. JJrit., 
XVII; Cancer muscosus / Lin.; — P. tetraodon, Leach, Ib. .x.x, 
II Pisa heros, Latr., Encyc. Method. 
Maia lavras, Lain. ; Cancer cornudo, llerbst., lix, 6. 
N.B. The genus Amathia of hi. P. Rou.\, Hist, des Crust, de la Mcditerr., &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 c.xecuted. 
