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Show 20 CRUSTACEA. •' FAMILY 1(1 ). BRACHYURA.-KL'EISTAGNATHA, 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 vulvre are two holes situated under the pectus, between the third pair of feet. The antennre are small: each of the intermediate ones, usually lodged in a fossula under the anterior edge of the shell, terminates in two very short filaments. The ocular pcdicles are generally longer than those of the Dec a poda Macrou ra. The auricular tube is almost always stony. The first pair of feet terminate in a forceps or claw. The bran~hire are disposed on a single range, in the form of pyramidal hgulre, 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 b:J.sed on an ensemble of important anatomical characters, and generally correspond to the Linna:an genera, and sometimes also to those established by Fabricius in his earlier works. These families are more e.xtensive than t?~ ~ections thus named in my other writings: but if they be consu. lered as first dlV!stOns of orders, and if what I have termed tribes be considered as families, .it. will be seen that the method is essentially the same. There is, ~hen,. the opmtons of others to the contrary notwithstanding, no real discrepance m this respect. On the same principle, the subgenera, with the exception of ~orne whose cl~aracters are too minute ot• too slightly marked, will become genera 1n a more detatled and special system. \2) The a~purent numbet· of segments, which is usually seven, sometimes also vartes ac~orchng to the sex; it is less in the females. Dr Leach has made gt·eat use <lf thts 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. DECAPOD A. 21 two external ones forming a sort of lip( I). Their nervous system also differs from that of the Macroura(2). . This family, as in several of the systems anterior to the distribution of these animals by Daldorf, might constitute but one genus, that of CANCER, Lin. In the greater number, all the feet are attached to the sides of the pectus, and are always exposed; this is the case in the first five sections. The first, or that of the PrNNIPEDEs(3), to this character, adds that of having the last feet, at least, terminated by a very flat or fin~ like joint that is oval or orbicular and broader than the same joint of the preceding feet, even when they also are shaped like a fin. They seldom frequent the coast, and are generally found in the high (1) Those of the lbcroura are longer and narrower. It is on this difference that Fabricius established his order of the Exocltnata. (2) See general observations on the Decapoda. (3) This systematic arrangement of the Brachyura is artificial, or but littl';?: natural in some respects; in consequence of which, we have somewhat altered it in our Famille:J Naturelles du Regne JJ.nimal. The QuADRILJ.TERA compose our first tribe, at the head of which are the Ocypoda and other Land-Crabs, ending with the River-Crabs, or the Telphusre. The Ancu.&TA form the second. That of the CnYl''l'OPODA appearing to us more closely allied to the preceding one than the TmANGULARIA, will immediately follow, and be the third, and not the fourth, as in this method. Immediately after the Arcuata we will place those genera whose claws are in the form of a crest, whose lateral a~tenn~ are always very short, and the third articulation of whose foot-jaws is triangular, and frequently entire, or without any emargination; such are the Hepati, Matutre, Ovithyire, and Mursim. Brachyura approaching the latter in the form of the same articulation, but whose claws differ, and where the lateral antenna: are salient, advanced, and frequently hairy, such as the Thire, Pirimelre, and .O.telecycli, will immediately precede these latter subgenera. As the Telphus~ seem to be connected with the Eriphire and the Pilumni, and as from these we naturally pass to C::mcet• properly so called, or the Cancer, Fab., it foUows that the Portuni and other natatory Ar· cuata should be at the head of this tribe. Then follow the O~tnrcuLAmA, the TnaNGULAlliA, and the NoTOPODA. But of these the Dromim and the Dorippe:J should be placed higher in the scale. The Homolre, Litlwde:J, and Raninre, appear to me to be of all the Brachyura, those which are most closely aUied to the Macrout ·a. The external foot-jaws of the Ilomol~ and of the Lithodes greatly resemble those of the Macroura by their length and projection. Although we have divided the Decapoda into two genera only, in order to conform to modem systems, and to diminish the number of subgenera, our sections may be converted into tribes, corresponding to as many subgenera, to be afterwards divided into various subgeneric sections. |