ORDER DECAPODA. 161 



globular or rhomboidal, or ovoid, and always very solid ; the 

 ocular pedicles are always short, or but little elongated ; the 

 claws are of unequal size, according to the sexes (larger in 

 the males) ; the tail never presents seven complete segments ; 

 the buccal cavity proceeds nan-owing towards its superior ex- 

 tremity, and the third articulation of the external jaw-feet is 

 always in the form of an elongated triangle. The posterior 

 feet resemble the preceding, and none of the latter is ever very 

 long. 



CoRYSTES, Latr., 



Have the testa in an oblong-ovoid figure, crustaceous, with 

 the lateral antennse long, advanced, and ciliate. The ocular 

 pedicles are of middle size, and apart ; and the third articula- 

 tion of the external jaw-feet is longer than the preceding, 

 with an apparent emargination for the insertion of the follow- 

 ing articulation. The tail consists of seven segments, but 

 two in the middle are obliterated in the males, Cancer per- 

 sonatuSy Herbst., Leach. 



Leucosia, i^f/i>., 



Have a testa, whose form varies, but is most generally almost 

 globular or ovo'id, and always of a very hard and stony con- 

 sistence. The lateral antennae and the eyes are very small ; 

 the eyes are approximate ; the third articulation of the exter- 

 nal jaw-feet is smaller than the preceding, and without ap- 

 parent internal sinus. These parts are contiguous inferiorly, 

 along the internal edge, and form an elongated triangle, whose 

 extremity is received in two upper lodges of the buccal cavity. 

 The tail very ample, and suborbicular in the females, usually 

 presents but four or five segments, but never seven. 



Dr. Leach has divided this genus into several others, but 

 which we shall present as simple divisions. 



VOL. XIII. M 



