OCR Text |
Show 104 CRUSTACEA. This subgenus leads us to those in which these organs are formed of granules or approximated si~~le eyes, an~ that also have the four antennre, composed of four JOints at ~ost, mserted. on one horj. zontal line and all the feet fitted for walkmg. The ta1l consists or six segme~ts, the last of which is large and suborbicular. Such is the LIMNORIA, Leach. The only living species known is the Limnoria terebram, Leach, Ed in b. Encyclop., VII, P· 433; Desmar., Consid., p. 312. Although scarcely above two lines in length, its habits and fecundity render .it highly noxious. It perforates the tim. hers of ships in various directions and with alarming rapidity. ':Vhen taken in the hand it rolls itself into a ball. It is found in various parts of the British seas. The figure and description of a small fossil crustaceous ani· mal has been sent to Count Dejean by Professor Germar, which seems to us to belong to this subgenus( 1 ). The third section-Sl'HlE!!.OMIDEs, Lat.-exhibits four very dis· tinct, short, setaceous or conical antennre, and a single genus-An· thura-excepted, always terminated by a stem divided into several small joints; the inferior, always the longest, are inserted beneath the under part of the first joint of the superior which is broad and thick. The arrangement of the mouth is as usual. The branchire are vesicular or soft, exposed, and arranged longitudinally in pairs. But two complete and movable segments are observed in the tail, the first, however, frequently presents impressed and transverse lines indicating vestiges of others; on each side of its posterior ex· tremity is a fin terminated by two leaflets, of which the inferior alone is movable; the superior(2) is formed by an internal prolongation of the common stem. The branchial appendages are curved in· wards; the inner side of the first are accompanied, in the male, by a small linear and elongated projection. The anterior part of the head situated beneath the antennre is triangular, or has the figure of a heart reversed. Some have an oval or oblong body, usually assuming, when con· tracted, the form of a ball; the antennre terminated by a pluri-articu· lated stem, and the inferior, at least, visibly longer than the head. ( 1) The Oniacua prreguatator, figured in Parkinson, is allied to this species, or at least appears to belong to the same section. (2) It folds over the posterior edge of the last segment, and in several, such as the Zuzarae, and N aesae, Leach, like an arch. ISOPOD A. 105 . 1 1 nd p' osterior fins are composed of a peduncle and two The atera a d l'k . ~ ming with the last segment a common fin shape 1 e a lammz, .or fanI.n th the impressed and transverse lines of the anterior seg· ese, f the tail which is always shorter than the next or last one, ment o ' · • f h · do not ex t en d to the lateral margin. The first JOlllt o t e su penor antennz has the form of a triangular palette. The bead, view.ed from above, forms a tra~sverse ds~uare: The leaflets of the fins are much flattened, and the mterme 1ate p1ece or the last segment is widened and rounded laterally. ZuzARA, Leach. Leaflets of the fins very large; the superior, which is the shortest, separates from the other to form a border to the last segment( 1 ). SPH.IEROMA, Lat. Leaflets of a moderate size, equal, and laid one over the other(~)· 1 those the impressed lines or transverse sutures of the anter10r seg:ent of the tail extend to its lateral edges and cut it. The first joint of the superior antennre forms an elongated square, or linear palette. • The leaflets of the fins are usually narrower and thicker than m the preceding; the external sometimes (Cymodocea~ incloses the other, which is prismatic ; the point at which they umte resembles a knot or joint. . . . Sometimes the sixth segment of the body 1s VlS1bly longer through-out all its width than the preceding ones and that which follows. Only one of the two leaflets projects. N.IEsA,-Campecopea, Leach(3). Sometimes the sixth segment of the body is as long as the preceding ones and as that which follows. CrLIO.JEA, Leach. Only one of the fin-leaflets salient, the other being placed against the posterior edge of the last segment( 4). (1) Deamar., Consid., p. 298. . (2) Desmar., Consid., p. 299-302. Spherome denUe, XLVII, 3;-0ntacuuer-ratw, Fab. (3) Desmar., Consid., Nule bidente, XLVII, 2;-Campecopee velue, Id., Jt., l. (4) Desmar., Conaid., Cilicee de Latreille, XLVIII, 3. VoL. III.-0 |