GASTEROPODA NUDIBRANCHIATA. 341 



Journ. de Phys., 1785, October, pi. ii. A large species of a 

 copper colour, from the coast of France. 



The same locality produces many others which vary greatly 

 in size and the form of their branchi£e(l)j several of them are 

 very small(2). 



Thethys, Lin. (3) 



Two rows of branchiae resembling branching tufts along the back, 

 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 jawsj on the base of the veil are two compressed 

 tentacula, from whose margin projects a small conical point. The 

 orifices of the genital organs, of the anus, and of the peculiar fluid 

 are situated as in the Tritoniae. The stomach is membranous and 

 the intestine very short. 



T. fimbria^ L.; Cuv., Ann. du Mus., XII, xxiv(4). Grey, 

 spotted with white; a beautiful species from the Mediterranean. 



ScYLL^A, 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 resem- 

 bling a little proboscis; orifices as in Thethys; the compressed ten- 

 tacula 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 branchiae. The middle of the stomach is invested with a fleshy 

 ring, internally armed with horny and trenchant laminae, like knives. 



(1) Such are Trit. elegans, Descr. de I'Eg., Zool., Gaster., pi. 2, f. \;—Trit. 

 rubra, Leuck., App. , Rupp., Invert, pi. 4, f. 1; — Tr. glauca, lb., f. 2; — T. cyano- 

 branckiata, lb., f. 3; — T. arhortsctns, Cuv., Ann. du Mus., VI, Ixi, and three 

 others, at least closely allied; — Dwis arborescens, Strzem., Act. Hafn., X, v, 5; — 

 Doris frondom, Ascan., Act. Dronth., V, v, 2, and Doris cervina, Bomme, Act. 

 Fless., I, iii, 1. 



(2) Dwis coronata, Bomme, lb., and Doris pinnatijida, Lin. Trans., VII, vii, 

 which is closely allied to it; — Doris fimbriata, Miill., Zool. Dan., CXXXVIII, 2, 

 and probably Doris dmigera, Mull., lb., XVII, 1 — 3. Perhaps the Doris lacera, 

 Zool. Dan., CXXXVIII, 3, 4, should also be referred to this genus. 



(3) From S-eS-uaiv, a name employed by the ancients to designate the Ascldiae; 

 Linnaeus applied it to this genus. 



(4) The difference observed between the Thethys Jimbriata, Bohatsch., Anim. 

 Mar., pi. v, and the 7' hethys leporina, Fab., Column., Ag., pi. xxvi, appears to me 

 to be the result of a greater or less degree of preservation. 



