310 CRUSTACEA. . 



rior and elongated appendage or branch, whicli seems to double their num- 

 ber. They are exclusively adapted for natation, and none of them termi- 

 nates in a forceps. The ova are situated between them, and not under tlie 

 tail. 



This genus is now divided into four sections each consisting of nume- 

 rous subgenera. In one of these [Pagurus) we find the Hermit {Cancer 

 Bernhardus, L.) which inhabits univalve shells, stopping the aperture with 

 its right claw, which is the largest. It is common in European seas. In an- 

 other (^sfac«s. Fab.) we find the Astacus marinus or Common Lobster. 

 The fresh water species are known by the name of Craw-Jish. Among these 

 also we find the Shrimp {Crangon) and the Prawns {Palxmon). 



ORDER II. 



STOMAPODA. 



The branchiae of the Stomapoda are exposed and attached to the 

 five pairs of sub-abdonninal appendages, exhibited to us by that part 

 of the body, called tail, in theDecapoda, and which here, as inmost 

 of the Macroura, are fitted for natation, or are fin-feet. Their shell 

 is divided into two portions, the anterior of which supports the eyes 

 and intermediate antennas, or composes the head, without giving ori- 

 gin to the foot-jaws. These organs, as well as the four anterior feet, 

 are frequently approximated to the mouth on two lines that converge 

 inferiorly, and hence the denomination of Stomapoda affixed to this 

 order. 



The teguments of the Stomapoda are thin, and in several nearly 

 membranous or diaphanous. The shell is sometimes formed of two 

 shields, of which the anterior corresponds to the head and the pos- 

 terior to the thorax, and sometimes of a single piece, which how- 

 ever is free behind, usually exposing the thoracic segments, bearing 

 the three last pairs of feet and having an articulation before that 

 serves as a base to the eyes and intermediate antennae; these latter 

 organs are always extended and terminated by two or three threads. 

 The eyes are always approximated. The formation of the mouth is 

 essentially the same as in the Decapoda; but the palpi of the man- 

 dibles, instead of being laid on them, are always vertical. The 

 foot-jaws are deprived of the flagelliform appendage presented to us 

 by the same parts in the Decapoda. They have the form of claws 



