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Show 100 CRUSTACEA. CYMODOOEA, Leach. Both leaflets salient and directed backwards ; the sixth segm~t is not prolonged posteriorly, and the extremity of ti]e last one pre. sents a small lamina in an emargination( 1 ). . DYNAMENE, Leach. Similar to the Cymodocere in the projection and direction of the leaflets of the fins, but the sixth segment is prolonged posteriorly, and the last one exhibits a mere fissure without the lamina(2). The others, such as the ANTHURA, Leach, Have a vermiform body, and the antennre, composed of four joints, scarcely as long as the head. The leaflets of the posterior fins by their disposition and approximation form a sort of capsule. The anterior feet are terminated by a monodactyle forceps(3). In the fourth section-InoTEIDEs, Leach-there are also four an· tenore, but they are placed on one horizontal and transverse line; the laterals terminate in a tapering, pointed, pluriarticulated stem; the intermediaries are short, filiform or slightly inflated at the end, and consist of four joints, neither of which is divided. The composition of the mouth is the same as in the preceding sections. The branchire, white in most of them, are in the form of bladders, sus· ceptible of inflation, serving for natation and covered by two lami· nre or valvulre of the last segment that adhere laterally to its edges; they are longitudinal, biarticulated, and open in the middle on a straight line like folding doors. The tail consists of three seg· ments, the last of which is much the largest, and has neither termi· nal appendages nor lateral fins. They are all marine. InoTEA, Fab. All the feet alike, and strongly unguiculated ; the body oval or simply oblong, and the lateral antennre shorter than half the length of the body( 4). (1} Desmar., Consid., XLVIU, 4. (2) Desmar., Cons.id., p. 297. (3) Desmar., Consid., .IJ.nthure grik, XLVI, 13; Oni&cw gr_~lu, Montag., Trans. Lin. Soc. IX, v, 6;-Gammarus htteroclitw, Vivian., Phosph. Mar., II, u. 12. . (4) 0ni3ctts entomon, L.; Squilla entomon, Deg., Insect., VII," xnii, 1, 2;ldotea tri~idata, Latr.; Desm., Consid., XLVI, ii. For the other speciea,tee ldotea, Nouv. Diet. d'Hist. Nat., Ed. II, anu Desmar. op. cit. ISOPOD A. 107 STENOSOMA, Leach. Th Stenosomre only differ from the Idotere in. the linear form of their ~ody, and the length of their antennre which is more than half that of the body( 1 ). ARcTuRus, Lat. The Arcturi are very remarkable for the form of the second and third feet, which incline forwards and terminate by a long, beard~d and unarmed or feebly unguiculated joint; the two anterior are la1d on the mouth and are unguiculated; the last six are strong, ambulatory, thrown behind, and bidentated at the extremity. In the length of the antennre and form of the body they approach the Ste-nosomre. I have never seen but a single species, the .IJ.rct. tuberculatus, which was brought to Europe, from the Arctic seas, in one of the last expeditions to those regtons. The fifth section-AsELLOTA, Lat.-comprises Isopoda with four very apparent setaceous antennre, arranged on two lines, and terminated by a pluriarticulated stem; two mandibles; £our jaws covered, as usual, by a kind of lip formed by the first foot-jaws; vesicular branchire, in pairs, covered by two longitudinal and biarticulated, but free leaflets; a tail composed of a single segment, without lateral fins, but with two bifid stylets, or two very short tubercular appendages on the '{lliddle of its posterior edge. Other lamelliform appendages, situated at its inferior base, which are now numerous in the males, distinguish the sexes. AsELLus, Geoff. Two bifid stylets at the posterior extremity of the body; eyes separated; the superior an tenore at least as long as the peduncle of the inferior ; the hooks at the end of the feet entire. The only species of this subgenus that is known-the .!J.selle d'eau douce, Geoff., Ins. II, :xxii, 2; Squille aselle, Deg., Insect., VII, xxi, 1; Des mar., Consid., XLIX, 1, 2; ldotea aquatica, Fab.,-is very abundant in fresh and stagnant waters as well as in the marshes, in the vicinity of Paris. Its gait, unless alarm· ed, is very slow. In the spring it issues from the mud in which (I) Stenoaoma lineare, Leach; Desmar. op. cit. lb. xlvi, 12;-Stenoloma kecticum, lb.;-l®tea fliridi&nma, Risso, Crust., UI, 8. For the other species, see Desmar. op. cit. · |