GASTEROPODA NUDIBRANCHIATA. 39 



the external margin; this margin is enlarged, and as the animal 

 renews it after each semi-whorl, the shell projects most on two oppo- 

 site lines, and has a compressed appearance. 



They feed on aquatic plants in the Archipelago of India*. 



The two following genera were among the Volutae. 



Auricula, Lam, 



Differing from all the preceding aquatic Pulmonea in the columella, 

 which is marked with wide and oblique flutings. Their shell is oval 

 or oblong, the aperture elevated as in Bulimus, and the margin tumid. 

 Several are large ; we are not certain whether they inhabit marshes 

 like the Lymntei, or their borders like the Succinese. 



Auricula myosotis. Drap. Ill, 16, 17; Carijch'mm myosotis, 

 Feruss. The only species in France ; the animal has but two 

 tentacvila, and the eyes are at their base ; from the shores of the 

 Mediterranean!. 



CoNvovuLus, Lam. — Melampes, Movtf. 



Projecting folds on the columella, as in the Auriculae, but the margin 

 of the aperture is not tumid, and the internal lip is finely striated ; 

 the general form of the shell is that of a cone, of which the spire forms 

 the base. They inhabit the rivers of the Antilles^. 



ORDER II. 



NUDIBRANCHIATA I!. 



The Nudibranchiata have neither shell nor pulmonary cavity, their 

 branchiye being exposed on some part of the back. They all are 

 hermaphroditical and marine animals, frequently swimming in a re- 

 versed position, with the foot on the surface, concave like a boat, and 

 using the assistance of the margin of their mantle and then tentacvda 

 as oars. In the 



* Helix scarabiTus, L. 



f Add, Valuta auris MuJce, L., Martini, II, xliii, 436 — 38; Chemn.,X, cxlix, 

 1395, 1396 ; — Volufa auris Jiid^e, L., Martini, II, xMv, 449 — 51 ; — Vol. auris Sileni, 

 Born., IX, 3 — 4 ; — Vol. glabra Mart II. xliii, 447, 448 ; — Vol. coffea, Chemn., IX, 

 cxxi, 1044. 



X Valuta minuta, L., Mart., II, xliii, f. 445, or Bulimus coniformis, Brug. ; — Bui. 

 monUe, Brug., Mart. lb., f. 444 ; — Bui. ovulus, Br., Mart., lb., 446. 



II My four first orders are united by M. de Blainville in what he terms a sub- 

 class, designating them by the name of Paracephalophora Monoica. He 

 makes two orders of my iV«(Zti/-««c/ii((/a ; in the first, or the Cyclobranchiata, 

 he places Doris and other analogous genera : in the second, or the Polybranchiata, 

 arc Trifonia and the following genera, which he divides into two families, according 

 to the presence of two or four tentacula. 



