OCR Text |
Show 90 CRUSTACEA. cal. At least two of their four anterior feet are usually terminated by a forceps. The vesicular bursce, in those where they have been observedthe Gammarince, Latr.-are situated at the exterior base of the feet, commencing with the second pair, and are accompanied by a small plate. The pectoral scales which enclose the ova are six in number. Sometimes the four antennce, although of different proportions in several, have a similar form and uses; the inferior have no resem. blance to feet nor do they perform their functions. A subgenus which we have established under the denomination of loNE, Lat., Only, however, from a figure given by Montagu-Oniscus thora. cicua, Trans. Lin. Soc., IX, III, 3, 4-exhibits very peculiar charac. ters which separate it from all others of the same order. The body consists of about fi(teen joints, but only distinguished by lateral tooth-like incisions. The four antennce are very short; those that are external, being longer than the other·s, are the only ones Yisible when the animal is seen on its back. Each of the two first segments of the body of the female is provided with two elongated, fleshy, flattened cir·ri resembling oars. The feet are very short, concealed under the body and hooked. The six last segments are furnished with lateral, fleshy, elongated, fasciculated append~ges, which are simple in the male and like oars in the female. At the posterior extremity of the body we also observe six simple, recurved appen· dages, two of which are larger than the others. The abdominal valves are very large, cover the whole inferior surface of the body, and form a sort of receptacle for the ova. This animal remains concealed under the shell of the Calinassa subterranea, on the side of which it forms a tumour. Montagu, having withdrawn one of these Crustacea from its domicil, kept it alive for several days. The female is always accompanied by the male, who fixes himself firmly to her abdominal appendages by means of his forceps. It is a rare animal which, in its habits, approaches the Bopyri( 1 ). All the ensuing Amphipoda have the segments of the body per· fectly distinct, throughout their whole extent; in neither sex nor in any of the species do we find those long oar-like cirri observed in the first of the Iones. (1) See Ann. des Sc. Nat., Decemb. 1826, XLIX, 10, the male-11, the fe. male. ( A?t(PHIPODA. 91 In the 1a t ter' when it exists, the .m ovable toe of the foot, termi- 1 .. db forceps is formed of a smg e JOint. nate Y a ' • h Of these I as t ' there are some whose supe.r ior antennce are muc f shorter t h an the inferior' and even th. a.n their peduncle; the stem o the latter is composed of numerous JOints. 0ROHESTIA, Leach. The secon d P' 1 eet of the male terminated by a large forceps, the bl toe long and somewhat curved; those of the female by two mova e . t . th toes. The third J'oint of the inferior antennce 1s at most Wice e length of that of the preceding ones( 1 ). T ALIPRus, Lat. Neither of the feet forming a forceps. The third joint of the .inferior antennce more than twice the length of that of the precedmg • ones• the antennce large and spinous(2). ln'the following, the superior antennce are never much shorter than the inferior. Some of them, furnished with elongated setaceous antennce terminated by a pluri-articulated ste~, an~ witho~t any remarka~le forceps, approach the preceding m the1r superiOr antennce, which are somewhat shorter than the inferior, and are removed fr·om t~ose that follow by the form of their head which is narrowed before mto a kind of snout. Such is ATYLus, Leach(3). All those which succeed have the superior antennce as long as the inferior, or longer; their head is not elongated into a snout. Here, as in the five following genera of Leach, the peduncle of the antennre is formed of three joints( 4). Some, in their superior antennce, present a character which is (1) Oniscus gammarellus, Pall., Spic. Zool., Fascic., IX, iv, 8; Cancer gamma-rwlittoreus Montag.; Desmar., Consid., p. 261, XLV, 3. l (2) Onisc' uslocu8ta, Pall., Spic. Zool., Fasc1· c. IX , 1· v, 7 ; Cancer gammarWJ sa ta-tor, Montag.; Desmar., Consid., XLV, 11. . (3) .B.tylus carinatus Leach, Zool. Misc., LXIX; Desmar., Consld., P· 2 6h2 ' XLV, 4; Gammarus c~rinatus, Fab. ;-G. nugax.'l ejusd.; Phipps, Voy. to t e North Pole, XII, 2? b assi (4) The third joint of the peduncle may be very small and thus ecome. • milatea to the following, or those of the stem; t h.I s ped unc1 e , as in the Dexammes, then appears to comn. st of but two J.O .m ts. A ccord 'm g t o the system of Leach t 11 ~: stem is understood to form another but compound joint. |