GASTEROPODA NUDIBRANCH1ATA. 41 



similar to those in Doris, are four, and sometimes six others, simply 

 pointed*. 



TRITONIA, Cuv. 



Have the body, the superior tcntacula and genital organs as in Doris ; 

 but the anus and the orifice through which the peculiar liquid is ex- 

 creted, are pierced on the right behind the organs of generation ; 

 the branchiae, which resemble little trees, are arranged along the sides 

 of the back, and the mouth, provided with broad membranous lips, is 

 armed inside with two horny and trenchant lateral jaws, which may 

 be compared to a pair of sheep-shears. 



Trit. Hombergii, Cuv., Ann. du Mus., I, xxxi, 1, 2, and the 

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

 per colour, from the coast of France. 



The same locality produces many others which vary greatly 

 in size and the form of their branchiae f ; several of them are 

 very small J. 



THETHYS, Lin. 



Have all 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 membra- 

 nous proboscis without jaws ; on the base of the veil are two com- 

 pressed 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||. Grey 

 spotted with white ; a beautiful species from the Mediterranean . 



SCYLL.EA, Lin. 



Have the body compressed ; the foot narrow and marked with a fur- 

 row which enables it to clasp the stems of the fuci ; no veil ; the 



* Doris quadrilineata, Mull., Zool., Dan., I, rvii , 46, and better, Ib., cxxxviii, 

 5 6; D. cornuta, Ib., cxlv, 1, 2, 3 ; D.ftaca, Lin. Trans., VII, vii. p. 84; 

 Polycera lincata, Risso, Hist., Nat., IV, pi. i. f. 5. 



f Sucb are Trit. clegans, Descr., de 1'Eg. Zool., Caster., pi. 2, f. 1 ; Trit. ntbra, 

 Lcuck., App., Rupp., Invert., pi. 4, f. 1 ; TV. (jlnuca, Ib., f. 2 ; T. ci/anoliranchiuta, 

 Ib., f. 3 ; T. arborescent, Cuv., Ann. du Mus., VI, Ixi, and three others, at least 

 closely allied; Doris arbor escens, Strain., Act., Hafn., X, v. 5 ; Doris frondosa, 

 Ascan., Act. Dronth., V, v, 2, and Doris cervina, Bomm<S Act., Fless., 1, Hi, 1. 



J Doris coronata, Bomme*, Ib., and Doris pinnatifida, Lin. Trans., VII, vii, which 

 Is closely allied to it ; Doris ftmbriata, Mull., Zool. Dan., CXXXVIII, 2, and pro- 

 bably Doris clangera, Mull., Ib., XVII, 13. Perhaps the Doris lacera, Zool. 

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



From S^vwr, a name employed by the ancients to designate the Ascidise ; Lin- 

 nnn* applied it to this genus. 



|| The difference observed between the Thelhys fimbriala, Bobatsch., Anim. Mar., 

 pi. v, and the Thethys Irporina, Fab., Column., Ag., pi. xxvi, appears to me to be the 

 result of a greater or less degree of preservation. 



