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Show 428 MOLLUSCA. The THALIJE, Brown, have a small crest or vertical fin near the posteriot· extremity of the back( 1 ). Of the SALPJE, properly so called, some have a gelatinous dark co. loured plate, in the substance of the mantle and above the viscel'al mass, which may be the vestige of a shell(2). In others it is a simple prominence, of the same nature as the rest of the mantle, but thicker(8). Others again have neither plate nor prominence, but their mantle is extended by points, and of these Some have a point at each extremity( 4). Others have two at the extremity nearest the mouth( 5), and even three or more( 6). Some have but a single one at this same extremity(7). The greater number is simply oval or cylindrical(S). In the AsciDIA, Lin.-They ton of the Ancients, The mantle and its cartilaginous envelope, which is frequently very thick, resemble sacs evet·ywhere closed, except at two orifices, which correspond to the two tubes of several bivalves, one serving to admit water and the other affording a passage to the fceces. The branchire form a large sac, at the bottom of which are the mouth and the vis- (1) Holothuria Thalia, Gm., Drown's Jam., xliii, 3;-H. caudata, lb., 4;-H. denudata, Encyc. Method., Vers., lxxxviii;-8alpa cristata, Cuv., Ann. du Mus., IV, lxviii, 1, figured under the name of Dagysa by Home, Lect. on Compar. Anat. II, lxiii;-8alpa pinnata, Forsk., xxv, B. (2) 8alpa scutigera, Cuv. Ann. du Mus., IV, lxviii, 4, 5, probably the same as the 8alpa gibba, Bose., Vers, II, xx, v. (3) 8alpa Tilesii, Cltv., loc. cit. ':3;-S. punctata, Forsk., xxv, C.;-S.pelagica, Bose., loc. cit., 4;-S. infundilmliformis, Quoy and Gaym., Voy. de Freycin., Zool. 74, f. 13. (4) 8alpa mcu"ima, Forsk., xxxv, A;-S. fusiformis, Cuv., loc. cit., 10, perhaps the same as Forsk., xxxvi;-S. rnucronala, lb., D;-S. aspcra, Chamisso, f. iv;- 8. runcinata, Id., f. v, G, H, I. But, according to the author, it is the aggregate generation of a species, of which the other generation is cylindrical. (5) Salpa dernocmtica, Forsk., xxxvi;-8. longicauda, Quoy and Gaym., loc. cit., pl. 73, f. 8;-8. constata, lb., f. 2. (6) Salpa tricuspis, lb., f. 6;-8. spinosa, Otto., Nov. Ac. Nat. Cur., t. pl. xlii, f. 1. (7) Holothuria zonaria, Gm., Pall., Spic., X, i, 17;-Titalia lingulata, Blumenb., Abb., 30. (8) 8alpa octofora, Cuv., loc. cit., 7; perhaps the same as the small Dagysre, Home, loc. cit., lxxiii, 1;-8. africana, FOJ·sk., xxxvi, C;-8. Jasciata, lb., D;- 8. confeder~ta, lb., A; perhaps the same as the 8. gibba, Bose., loc. cit., 1, 2, 3;- 8. polycrattca, lb., F;-8. cylindrica, Cuv., loc. cit., 8 and 9;-Dagysa strumosa. Home, I, c., lxxi, 1;-8. fe:rruginea, Chamiss., X;-8. c:erulescens, Id., ix;-S. va· ginata, Id., vii, and several others. ACEPHALA NUDA. 429 ceral mass. The envelope is much larger than the mouth, which is fibrous and vascular, and on which, between the two tubes, is one of the ganglions. These animals attach themselves to rocks and other bodies, and are deprived of all power of locomotion; the chief sign of vitality which they exhibit, consists in the absorption and evacuation of water through one of their orifices; when alarmed they eject it to a considerable distance. Th.ey abound in every sea, and some of them are eaten( 1 ). Some species are remarkable for the long pedicle which supports tbem(2). FAMILY II. AGGREGATA. The second family consists of animals more or less analogous to the Ascidire, but united in a common mass, so that they seem to communicate organically with each other, and in this respect to connect the Mollusca with the Zoophytes; but independently of their peculiar organization, these animals, according to the observations of Messrs Audouin and Milne Ed- (1) The whole genus Ascmu, Gm., to which must be added the .B.sc. gelatino1a, Zool. Dan., xliii;-.B.sc. pyr-iformis, lb., clvi;-Salpa siplw, Forsk., xliii, C;-.B.scidia microsma, Redi, Opusc., III, Pl., App., Vll, the same as the .B.sc. sulcata, Coquebert, Bullet. des Sc. Avril, 1797, I, 1 ;-.B.sc. glandiformis, Coqueb., Ib.-N.B. The .ll.acidia canina, Mull., Zool. Dan., lv, .B.sc. intestinalis, Bohatsch, X, 4, and perhaps even the .B.sc. patula, Mull., lxv, and .11.. corrugata, Id., lxxix, 2, appear to form but one species. There are also some interversions of synonymes, and the species, generally, are far from being well ascertained. l\1. de Savigny has endeavoured to subdivide the Ascidia:, Mem. sur les Anim. sans vert., part II, 1816, into several subgenera, such as, 1st. The CYNTIII.iE, whose body is sessile and branchial sac longitudinally plicated; their envelope is coriaceous; 2d. The PHALLUSIJE, which differ from the Cynthia: in the branchial sac which is not plicated; their envelope is gelatinous; 3d. The CLAVELLIN.iE, whose branchial sac is without plica:, and does not penetrate to the bottom of the envelope, and whose body is supported by a pedicle; their envelope is gelatinous; 4th. The BoLTENl.IE, whose bocly is pediculate, and the envelope coriaceous. He also takes into consideration the number and form of the tentacula which internally surround the branchial orifice, but these character~, which are partly anatomical, cannot be applied wi\h certainty to a great number of species. M. Macleay (Lin. Trans., XIV, part III) establishes two more, CYSTJNGIA and DE:Nnnono.A, founded on similar characteTs. (2) .llscidia pedunculata, Edw., 356; and .llsc. clavata, or Vorticella Boltenii, Gm. |