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. Tnachus dorsettensis, Leach.) 



AcHiEUS, Leachy 



Have all equally six segments in the tail ; but their four pos- 

 terior tarsi are very much arched, or like a reaping hook ; 

 their ocular pedicles are always projecting, and present a 

 tubercle in front. {Achcsus 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 antennae is removed, 

 by a notable space, from the superior edi^e 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. 



Stenorhynchus, Lam., Macropodia, Leach, 



Have six segments to the tail in both sexes. The anterior 

 extremity of the testa is bifid. {Macropodia tenuirostris, 

 Leach .) 



Leptopodia, Leach. 



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. {Tnachus Sagit- 

 tarius, Fab.) 



The last trigona differ from the preceding, in the dissimi- 

 larity of the posterior feet. 



