GASTEROPODA NUDIBRANCHIATA. 255 



Thethys, Lin. 



Two rows of branchiae resembling- branching tufts along the bact, and a very 

 large membranous and fringed veil on the head, which shortens as it curves 

 under the mouth: this latter is a membranous proboscis without jaws; on the 

 base of tlie veil are two compressed tentacula, from whose margin projects 

 a small conical point. 



T. fimbria, L. Grey, spotted with white; a beautiful species from the 

 Mediterranean. 



ScYLLiEA, Lin. 



Body compressed; the foot narrow and marked with a furrow which enables 

 it to clasp the stems of the fuci; no veil; the mouth resembling a little pro- 

 boscis; orifices as in Thethj'^s; tlie compressed tentacula terminated by a 

 cavity, from which issues a little uneven point, and two pairs of membranous 

 crests on the back, the internal surface of which is furnished with pencils 

 of filaments, which are the branchise. The middle of the stomach is invested 

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

 knives. 



S.pelagka, L. Common on all the floating fucus of almost every sea. 



Glaucus, Forster. 



Body elongated; four very small conical tentacula, and on each side three 

 branchiae, each of which are formed of long slips arranged like the sticks 

 of a fan, which also aid them in swimming. They are beautifid little ani- 

 mals that inhabit the Mediterranean and the Atlantic, prettily coloured with 

 blue and nacre; they swim on their back with great swiftness. 

 The remaining genera of this order are Laniogerus, Eolidia, CavoUna, &c. 



ORDER III. 



INFEROBRANCHLA.TA. 



The Inferobranchiata have nearly the same form and organiza- 

 tion observed in Doris and Tritonia, but their branchiae, instead of 

 being placed on the back, resemble two long series of laminas, situ- 

 ated on the two sides of the body, under the projecting margin of 

 the mantle. 



Phtllidia, Cuv. 

 The mantle naked, usually coriaceous, and without any shell; the mouth, a 

 small proboscis, eachside of which is furnished with a tentaculum; two others 



