ORDER DECAPODA. 
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compressed, but not forming a fin, properly so called. Those 
among them whose testa is broader, cut in front like the arch 
of a circle, narrowed and truncated behind, whose claws are 
identical in the two sexes, in which the tail presents the same 
number of segments as in portunus, and which, with the ex- 
ception of the tarsi, almost entirely resemble the last-men- 
tioned genus, shall compose our second section, that of 
Arcuata. 
The Crabs, properly so called, (Cancer, Fab .,) 
Have the third articulation of the external jaw-feet notched 
or marked with a sinus, near the internal extremity, and 
almost squared. The antennae, but little exceeding the front, 
and with but few articulations, are folded, smooth, or but little 
furnished with hairs. The hands are rounded, and do not 
present the appearance of a ridge above. 
Some have the radical articulation of the external antennae 
much larger than the following, in the form of a lamina, ter- 
minated by a projecting and advanced tooth, closing inferiorly 
the internal corner of the ocular cavities. The fossets of the 
middle or internal antennae are almost longitudinal. Such 
is C.pagurus , Lin. which Dr. Leach separates generically 
from other crabs. 
In the others, the inferior articulations of the antennae are 
cylindrical. The first, although a little larger, does not differ 
from the following as to form and proportions, and does not 
pass the internal canthus of the ocular fossets. Those of the 
intermediate antennae extend rather in the direction of the 
breadth of the testa, than in that of its length. 
There are some among them whose toes have their extre- 
mity hollowed like a spoon, (C. dentatus, Fab.) These are 
the clorodius of Dr. Leach. Many of these species in which 
they terminate in a point are remarkable, inasmuch as the 
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