OCR Text |
Show 96 CRUSTACEA: PRANIZA, Leach. Four setaceous antennre, as in the preceding; but the thorax viewed from above presents but three segments, the two first of which are very short and transverse, each supporting a pair of feet, while the third, much larger and longitudinal, supports the others. The feet are simple; the head is triangular, pointed before, and has prominent eyes. Each side of the posterior extremity of the body is also provided with a fin( 1 ). Various genera of Messrs Savigny, Rafinesque and Say(2), but the characters of which have not been described or sufficiently de· veloped, appear to belong to this order of the Amphipoda. Even some of the subgenera I have just quoted, require to be re-examined. M. Milne Edwards has made several valuable and detailed obser· vations on several of these Crustacea, which will most certainly tend to elucidate the subject. ORDER IV. L.tEMODIPODA. The Lremodipoda are the ·only Malacostraca with sessile eyes, in which the posterior extremity of the body exhibits no distinct branchire, and which are almost deprived of a tail, the two last feet being inserted in that extremity, or the seg· ment which connects them with it being merely followed by one or two very small joints. They are also the only ones in which the two anterior feet, that correspond to the second foot-jaws, form part of the head. They all have four setaceous antennre supported by a triar· (1) Oniscm creruleatus, Montag., Trans. Lin. Soc., XI, iv, 2; Encyclop. Method., Atl. d'Hist. Nat., CCCXXIX, 28, and CCCXXIX, 24, 25; Desmar. Consid., XLVI, 8. (2) I can say nothing of the G. ergine, Risso: the number of its feet would seem to place it in the last section of the Amphipoda; while the manner in which they terminate, and the number of the segments of the body, appear to throw it among the lsopoda. L.iEMODlPODA. 97 ticulated peduncle, mandibles, without palpi, a vesicular body at the base of at least the four pairs of feet, beginning at the second or third pair, those of the head included. The body, usually filiform or linear, is composed of eight or nine segments, including the head, and some small appendages in the form of tubercles at its posterior and inferior extremity. The feet are terminated by a stout hook. The four anterior, the second of which are the largest, are always terminated by a monodactyle forceps or a claw. In several, the four following ones are shortened, less articulated, without the terminal hook, or are rudimental, and nowise adapted for the ordinary uses of similar parts. The females carry their ova under the second and third segments of the body in a pouch formed of approximated scales. They are all marine Crustacea. M. Savigni considers them as allied to the Pycnogonides, and constituting with the latter the transition from the Crustacea to the Arachnides. In the first edition of this work they formed the first section of the Isopoda, that of the Cistibranchiata. We may unite them in a single genus which, by the law of priority, should be called the Cv A Mus, Lat. Som.e-the FrLIFORMA, Lat.-have a long and very slender or linear body with longitudinal segments; feet equally slender and elongated, and the stem of the antennre composed of several small joints. They are found among marine plants, walk like the caterpillar termed the Geometra, sometimes rapidly revolving in a circle, or turning up their body, during which time the antennre are vibrating. While swimming, the extremities of their body are curved. LEPTOMERA, Lat.-Proto, Leach. Fourteen feet, including the two annexed to the head, all complete and in a continuous series. Here, as in our LEPTOMERA proper-Gammarus pedatus, Mull., Zo~l. Dan., CI, 1, 2-all the feet, the two anterior excepted, have a vesicular body at their base. There, as in the PRoTo, Leach-Cancer pedatus, Montag., Trans. VoL. III.-N |