ORDER DECAPODA. 
171 
but little arched ; the ocular pedicles even susceptible of 
being concealed in their fossets, and a tooth or spine, in the 
males at least, at the posterior edge of these cavities. Dr. 
Leach has greatly contracted the primitive extent of this 
group. ( Cancer dodecos ? Linn. Inachus dorsettensis , Leach.) 
AcHiEUS, Leach , 
Have all equally six segments in the tail ; but their four pos- 
terior tarsi arc very much arched, or like a reaping hook ; 
their ocular pedicles are always projecting, and present a 
tubercle in front. ( Achcem cranchii , Leach.) 
Next come those whose epistoma is longer than broad, in 
the form of a triangle, elongated and truncated at the summit, 
and in which the origin of the middle antenna) is removed, 
by a notable space, from the superior edge of the buccal 
cavity ; the ocular pedicles are always projecting, when the 
testa is triangular and terminated in a point, more or less 
bifid, or entire. 
Stenorh YNCHUS, Lam., Macropodia , Leach, 
Have six segments to the tail in both sexes. The anterior 
extremity of the testa is bifid. (. Macropodia tenuirostris , 
Leach.) 
Leptopodia, Leacli. 
The tail of the males is composed of five segments ; that of 
the females has one more. The testa is prolonged anteriorly 
into a long, entire, and denticulated point. (. Inachus Sagit- 
tarius, Fab.) 
The last trigona differ from the preceding, in the dissimi- 
larity of the posterior feet. 
