428 MOLLUSCA. 



The Thali.e, Brown, have a small crest or vertical fin near the 

 posterior extremity of the back(l). 



Of the Salp.e, properly so called, some have a gelatinous dark co- 

 loured plate, in the substance of the mantle and above the visceral 

 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(3). 



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(8). In the 



AsciDiAj Lin. — Theyton of the Ancients, 



The mantle and its cartilaginous envelope, which is frequently very 

 thick, resemble sacs everywhere 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 faeces. The branchiae 

 form a large sac, at the bottom of which are the mouth and the vis- 



(1) Holothuria Thalia, Gm., Urown's Jam., xliii, 3; — H. caudata, Ih., 4; — ff. 

 denudata, Encyc. Method., \'ers., Ixxxviii; — Salpa cristafa, Cuv., Ann. du Mus., 

 IV, Ixviii. 1, fig-ured under the name of Dagysa by Home, Lect. on Compar. 

 Anat. II, Ixiii; — Salpa pinnata, Forsk., xxv, B. 



(2) Salpa scuiigera, Cuv. Ann. du Mus., IV, Ixviii, 4, 5, probably the same as 

 the Salpa gibbp, Bosc, Vers, II, xx, v. 



(3) Salpa Tilesii, Cuv., loc. cit. 3; — 5*. punctata, Forsk., xxv, C; — S. pelagica, 

 Bosc, loc. cit., 4; — S. infundibuliformis, Quoy and Gaym., Voy. de Freycin., 

 Zool. 74, f. 13. 



(4) Salpa maxima, Forsk., xxxv. A; — S. fusiformis, Cuv., loc. cit., 10, perhaps 

 the same as Forsk., xxxvi; — S. mucronala, lb., D; — (S*. aspera, Chamisso, f. iv; — 

 S. runcinata. Id., f. v, G, H, I. But, according* to the author, it is the aggregate 

 generation of a species, of which tlie other generation is c}lindrical. 



(5) Salpa democratica, Forsk., xxxvi; — S. longicauda, Quoy and Gaym., loc. cit., 

 pi. 73, f. 8;— 5. constata, lb., f. 2. 



(6) Salpa tricuspis, lb., f. 6; — S. spinosa, Otio. , Nov. Ac. Nat. Cur., t. pi. 

 xlii, f. 1. 



(7) Holothuria zonaria, Gm., Pall., Spic, X, i, 17,- — T/ialia lingukita,'Bhimenh., 

 Abb-, 30. 



(8) Salpa octofora, Cuv., loc. cit., 7; perhaps the same as the small Bagyaae, 

 Home, loc. cit., Ixxiii, 1; — S. africana., Forsk., xxxvi, C; — <S'. fasciata, lb., D; — 

 S. confederata, lb.. A; perhaps the same as the S. gibba, Bosc, loc. cit., 1, 2, 3; — 

 S. polycratica, lb., F; — S. cylindrica, Cuv., loc. cit., 8 and 9; — Dagysa strumosa. 

 Home, 1, c, Ixxi, 1; — S. ferruginea, Chamiss., X; — S. casrulescens. Id., ix; — S. va- 

 ginata. Id., vii, and several others. 



