20 CRUSTACEA, 



FAMILY 1(1). 

 BRACHYURA.— Kleistagnatha, Fab. 



Tail shorter than the trunk, without appendages or fins at 

 the extremity, and doubled under, in a state of rest, when it 

 is received in a fossula on the chest. Triangular in the males, 

 and only furnished at base with four or two appendages, in the 

 form of horns, the superior of which are the largest, it becomes 

 widened, and convex in the females(2), presenting beneath 

 four pairs of double hairy filaments(3), destined to support 

 the ova, and analogous to the sub-caudal natatory feet of the 

 Macroura, and others. 



The vulvai are two holes situated under the pectus, between 

 the third pair of feet. The antennae are small : each of the 

 intermediate ones, usually lodged in a fossula under the ante- 

 rior edge of tlie shell, terminates in two very short filaments. 

 The ocular pedicles are generally longer than those of the 

 Decapoda Macroura. The auricular tube is almost always stony. 

 The first pair of feet terminate in a forceps or claw. The 

 branchiae are disposed on a single range, in the form of pyrami- 

 dal ligulsB, composed of a multitude of leaflets piled one on 

 another, in a direction parallel to their axis. The foot-jaws are 

 generally shorter and broader than in the other Decapoda, the 



(1) The sections thus named are based on an ensemble of important anatomical 

 characters, and generally correspond to the Linnxan genera, and sometimes also 

 to those established by Fabricius in his earlier works. These families are more 

 extensive than the sections thus named in my other writings: but if they be con- 

 sidered as first divisions of orders, and if what I have termed tribes be considered 

 as famihes, it will be seen that the method is essentially the same. There is, 

 then, the opinions of others to the contrary notwithstanding, no real discrepance 

 in this respect. On the same principle, the subgenera, with the exception of 

 some whose characters are too minute or too slightly marked, will become genera 

 in a more detailed and special system. 



(2) The apparent number of segments, which is usually seven, sometimes also 

 varies according to the sex; it is less in the females. Dr Leach has made great 

 use of this consideration, which appears to us of but little importance, and opposed 

 to the natural order. 



(3) Several of these filaments exist in the males, but in a rudimental state. 



