ORDER DECAPOD A. 
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 narrowing 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, Lair., 
Have the testa in an oblong-ovoid figure, crustaceous, with 
the lateral antennae 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- 
sonatus , Herbst, Leach. 
Leucosia, Fab., 
Have a testa, whose form varies, but is most generally almost 
globular or ovoid, 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 interiorly, 
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 di visions. 
VOL. XTir. 
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