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 the 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, Avhich, according to Desmarest, — Hist. Nat. des Crust. 

 Foss., p. 125, is closely related to the mcenas. 



In the Portunus Rondeletii, Risso, there are no teeth in 

 front. The one he calls longipes, presents the same character, 

 but its feet are longer in proportion than those of other ana- 

 logous species. 

 We Avill form a fourth division with the subgenus. 



Platyonichus, Lat. 



Which name has replaced that of Portumnxis, Leach, on account 

 of the too great similarity between the latter and the Avord 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 III, 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 whose feet all terminate in a 

 point, or conical and sometimes compressed tarsus, but 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 Avhich, 

 with the exception of the tarsi, almost completely resemble them, 

 Avill constitute our second section, that of the Arcuata. In the 



Cancer, Fabr. 



Or the Crab 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 but slightly hairy. The hands are rounded and have no 

 appearance of a crest on the upper edge. 



The radical joint of the external antennje 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 article Platyonique, Encyc. Methodique, 



