GASTEROPODA TECTIBRANCHIATA. 257 



above the former. The branchiae are on the back, and consist of highly 

 complicated lamellse attached to a broad membranous pedicle, covered by 

 a small membranous mantle, in tlie thickness of which is a flat and horny 

 shell. A hmpid humour, secreted by a particular gland, and which in cer- 

 tain species is said to be extremely acx'id, is exuded through an orifice be- 

 low on the right, and from the edges of the mantle oozes an abundant liquid 

 of a deep purple colour, with which, when in danger, the animal tinges 

 the water for a considerable extent. The ova are deposited in a kind of 

 long, interlaced glairy net work, of extreme tenuity. In the seas of Europe 

 we have the 



Apl. fasciata, black, margined with lateral red crests, one of the large 

 species; and jlpl. punctata, Cuv., lilac, sprinkled with greenish points. 



DoLABELLA, Lam. 

 The Dolabellae only differ from Aplysise in the position of the branchiae and 

 their surrounding envelope; they are at the posterior extremity of the body, 

 which resembles a ti-uncated cone. They are found m the Mediterranean 

 and in the Indian Ocean. 



NOTABCHTJS, Cuv. 

 The lateral crests united and covering the back, a longitudinal emarginatlon 

 excepted, that leads to the branchiae, v/hich have no mantle to cover them, 

 but are otherwise like those of the Aplysise; the rest of their organization is 

 always the same. 



Akeba, Muller. 

 The branchiae covered as in the preceding genera, but their tentacula are so 

 shortened, widened and separated, that they seem to be totally wanting, or 

 rather to form a large, fleshy, and nearly rectangular shield, under which 

 are the eyes. The shell, of such as have any, is more or less convoluted, 

 but with httle obUquity, and is without a projecting spire, emarginatlon, or 

 canal; the columella, projecting convexly, gives a crescent-like figure to the 

 aperture, the part opposite to the spire being always the broadest and most 

 rounded. 



M. de Lamarck names those in which the shell is concealed in the thick- 

 ness of the mantle, Buli.ea. It has but very few whorls, and the animal is 

 much too large to be drawn into it. 



Bullxa aperta, Lam. The animal is whitish, and about an inch long; the 

 fleshy shield, formed by the vestiges of its tentacula, the lateral swellings 

 of its foot, and the mantle occupied by the shell, seem to divide its upper 

 surface into four lobes. Its thin, white, semi-diaphanous shell, is nearly all 

 aperture, and its gizzard is ai'med with three very thick rhomboidal pieces 

 of bone. It is found in almost every sea, where it lives on oozy bottoms. 

 The 



2 H 



