166 
CRUSTACEA. 
peculiar genus for it called Carcinus, (Malac. Brit., XII, tab. v) 
It also has five teeth on each side, and a similar number in front 
the internal oculars included. The top of the shell is glabrous’ 
finely shagreened, with deeply impressed lines. The tarsi are 
striate ; the upper edge of the hand is so compressed as to form 
a rounded ridge, terminated by a small tooth; a second but 
stronger one is observed on tlie inner side of the preceding joints ; 
fingers striate, and almost equally dentated, with a blackish tip. 
A fossil species is found in the marly limestone of Monte- 
Bolca, which, according to Desmarest, — Hist. Nat. des Crust. 
Foss., p. 12.5, is closely related to the moenas. 
In the Portunus Rondeletii, Risso, there are no teeth in 
front. The one he calls loncfipes, presents the same character, 
hut its feet are longer in proportion than those of other ana- 
logous species. 
We will form a fourth division with the subgenus. 
Platyonichus, Lat. 
Which name has replaced that of Portumnus, Leach, on account 
of the too great similarity between the latter and the word Portunus 
already adopted. Here the shell is at least as long as it is broad, and 
almost cordate. All the tarsi of the feet, the claws excepted, termi- 
nate in a small, semi-elliptical, elongated and pointed lamina ; the 
index is strongly compressed. 
This division also comprises but a single species, the Cancer 
latipes, Plancus, — De Conchis minus notis HI, 7? B, C, — and 
which has also been figured by Leach — Malac. Brit., IV. There 
are three front teeth, and on each lateral edge five*. 
From the swimmers we pass to those rvhose feet all terminate in a 
point, or conical and sometimes compressed tarsus, hut never form- 
ing a fin properly so called. Those of them whose shell is tapering, 
forming the arc of a circle before, and narrowed and truncated be- 
hind, in which the claws of both sexes are alike, where the number 
of the caudal segments is the same as in the Portuni, and which, 
with the exception of the tarsi, almost completely resemble them, 
will constitute our second section, that of the Arcuata. In the 
Cancer, Fabr. 
Or the Ci’ab properly so called, the third joint of the external 
foot-jaws is emarginated or marked with a sinus near the internal 
and almost square extremity. The antennae scarcely extending be- 
yond the front and composed of but few articulations, are flexed and 
glabrous, or hut slightly hairy. The hands are rounded and have no 
appearance of a crest on the upper edge. 
The radical joint of the external antennae is, in some, much larger 
than the following ones, and resembles a laminae ; terminated by a 
salient and advanced tooth, closing inferiorly the internal corner of 
See the artiele Plafyonique, Encye. Methodique. 
