ORDER DECAPODA. 187 



The two anterior claws are larger ; the lateral leaves of the 

 fin terminating the tail are in the form of an inverted triangle 

 or broader at the posterior edge. The intermediate, on the 

 contrary, grow narrow from the base to the end, and proceed 

 into a point. 



Callianassa, Leach, 



Have the claws very unequal, as well both in form as propor- 

 tions; the carpus of the largest of the two anterior is trans- 

 verse, and forms with the forceps a common body. The same 

 articulation of the other claw is elongated. The two posterior 

 feet are almost didactylous. The external leaf of the lateral 

 fins of the end of the tail is larger than the internal, with a 

 crest or ridge ; this last is even. 



The ocular pedicles are in the form of a scale or shell, and 

 the cornea is situated near the middle of their external edge. 

 The threads of the middle antennas are but little longer than 

 their peduncle. {Callianassa suhterranea, Leach.) 



Axius, Leach, 



Differ from them in their claws, which are almost equal, and 

 in which the carpus makes no part of the forceps ; the pos- 

 terior feet are similar to the preceding. The leaves of the 

 lateral fins are almost of the same size, and have each a 

 longitudinal crest ; the threads of the middle antenna? are 

 evidently longer than their peduncle. {Axiiis stirhynchus, 

 Leach.) 



Our second, and last subdivision, presents Crustacea, in 

 which the six anterior feet form so many claws, terminating 

 in a forceps perfectly didactylous, a character which dis- 

 tinguishes them from all the preceding decapods, and which 

 approximates them to the first of the following section ; but 

 here the claws of the third pair are the largest, instead of 

 which, in the others, it is the first two, and their thickness, 



