DECAPODA. 37 



second and fifth; the tarsi are marked with dentated or very spinous 

 ridges. They form two subgenera. 



Cardisoma, Lat. 



The four antennas and all the joints of dhe. external foot-jaws 

 exposed; the three first joints of these same foot-jaws straight; 

 the third shorter than the second, emarginated superiorly and 

 nearly cordiform; the first of the lateral antennae almost similar and 

 broad. 



They are called Crabes blancs at the Antilles, though sometimes 

 they have a yellow shell striped with red(l). 



Gecarcinus, Leach. 



The four antennae covered by the clypeus; second and third joints of 

 the external foot-jaws, large, flattened, arcuated, and leaving a space 

 between their inner sides, the last one forming a curvilinear trian- 

 gle, obtuse at the summit; it reaches to the clypeus, and covers the 

 three following ones, or the fourth, fifth, and sixth. 



The most common species — Cancer ruricolciyh.^ Herbst., Ill, 

 36, when young, IV, xx, 116; xlix, 1, is of a more or less 

 lively blood-red colour, more or less extended, and sometimes 

 spotted with yellow with a deeply marked impression of the 

 letter H. It is the Crabe violet, and Crabe pemt of travellers; 

 the name of Tourlourou appears to me to be more peculiarly 

 applied to this species(2). 

 Sometimes the shell is nearly square, subisometrical or not, 

 broader than it is long, flattened, and the front turned down for 

 nearly the whole of its width. The ocular pedicles are short and 

 inserted at the anterior lateral angles. The two ordinary divisions 

 of the intermediate antennae are very distinct. The inner sides of 

 the exterior foot-jaws are separated, leaving an angular space be- 

 tween them; their third joint is almost as long as it is broad. The 



(1) Cancer cordatus, L.; — Cancer carnifex, Herbst., XLI, 1, IV, 27; — C. guan- 

 Aumi, Marcgrave. The tarsi have four ridges; there are two additional ones in the 

 Gecarcini. 



(2) See the article Tourlourou in the Encyc. Methodique. Messrs Audouin 

 and Edwards have lately communicated to the Acad. Roy. des So. , some very 

 curious remarks upon an organ peculiar to these animals, which forms a sort of 

 reservoir capable of containing a certain quantity of water, and placed imme- 

 diately above the branchiae. This accounts for the unusual convexity of the ante- 

 rior sides of their thorax. 



