ORDER DECAPODA. 151 



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, Fah.,) 



Have the third articulation of the external jaw-feet notched 

 or marked with a sinus, near the internal extremity, and 

 almost squared. The antenna?, but little exceeding the front, 

 and with but few articulations, are folded, smooth, or but little 

 fmiiished 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 antennge are almost longitudinal. Such 

 is C pagurus, Lin. which Dr. Leach separates generically 

 from other crabs. 



In the others, the inferior articulations of the anteinia? 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. dentaius, Fab.) These are 

 the clorodius of Dr. Leach. Many of these species in which 

 they terminate in a point are remarkable, inasmuch as the 



13 



