42 MOLLUSC A. 



mouth resembling a little proboscis ; orifices as in Thethys ; the com- 

 pressed tentacula terminated by a cavity, from which issues a little 

 uneven point, and two pairs of membranous crests on the back, the in- 

 ternal surface of which is furnished with pencils of filaments, which 

 JHV the branchiae. The middle of the stomach is invested with a 

 fleshy ring, internally armed with horny and trenchant laminae, like 

 knivos. 



S. pelagica^ L. ; Guv., Ann. du Mus., VI, Ixi, 1, 3, 4. Com- 

 mon on the floating focus of almost every sea. 



GLAUCUS, Forster. 



Have the body elongated, and the orifices of the anus and of the 

 genital organs as in the preceding; four very small conical tentacula, 

 and on each side three branchiae, each of which is formed of long 

 slips arranged like the sticks of a fan, which also aid them in swim- 

 ming. They are beautiful little animals, that inhabit the Mediter- 

 ranean and the Atlantic, prettily coloured with blue and mother-of- 

 pearl ; they swim on their back with great swiftness. Their anato- 

 mical structure is very similar to that of the Tritonia, but the species 

 are not yet well ascertained*. 



LANIOGERUS, Blainv. 



Have on each side two series, of small and finely pectinated laminae, 

 which are the branchiae ; the body shorter and thicker than that of a 

 Glaucus, but there are four small similar tentacula.f 



EOLIDIA, CUV. 



Have the form of a small Limax, with four tentacula above, and two 

 on the sides of the mouth; the branchiae are composed of laminae, ar- 

 ranged like scales, more or less crowded, on each side of the back. 

 Found in every seaj. 



CAVOLINA, Brug. 



Have the tentacula of the Eolidiae, with radicating retiform branchiae, 

 arranged in transverse rows on the back||. 



* Doris radiata, Gm., Dup., Phil. Trans., LTI1, pi. Hi; Scyltte macree, Bosc., 

 Hist, des Vers ; Glaucus atlanticits, Blumenb., fig., Nat. Hist., pi. 48, and Manuel., 

 fr. trans., II, p. 22; Cuv., Ann. du Mus. VI, Ixi, ii, Peron, Ann. Mus. XV, 

 iii, 9. 



f Laniogerus Elfortii, Blainv., Malac, pi. xlvi, f. 4. 



j Dons papillosa, Zool. Dan., CXLIX, 1 4; Doris bodoensis, Gunner., Act. 

 Hafn., X, 170 Doris minima, Forsk., Ic., xxvi, H ; Doris fasiculata, Id., Ib., G; 

 Doris branchiate, Zool. Dan. CXLIX, 5 7 ; Doris cxrulea, Lin. Trans., VII, 

 vii. 84 ;Eolidia histrix, Otto., Nov. Act. Nat. Cur., IX, xxxviii, 2, &c. 



|| Doris peregrina, Gm., Cavolini, Polyp. Mar., VII, 3 ; Eolidia annulicornis, 

 Chumisso, Nov. Act. Nat. Cur., XI, part II, pi. xxiv, f. 1 ; Doris longicurnis, Lin. 

 Trans., IX, vii, 114. 



N.B. This genus must not be confounded with the Cavolina of Abildgard, which is 

 the 



