GASTEROPODA TKCTIBRANCHIATA. 1 / 



dinal emargination excepted, that leads to the branchiae, which have 

 no mantle to cover them, but are otherwise like those of the Aplysiae 

 as well as the rest of their organization J. In the^ 



BURSATELLA, BlaiUV . 



The lateral crests are united in front in such a manner as only to leave 

 an oval aperture for the transmission of water to the branchiae, which 

 are also deprived of a protecting mantle*. 



These two genera, however, probably form but one. 



AKERA, Muller. 



Have their 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 rec- 

 tangular shield, under which are the eyes. Independently of this, 

 the hermaphroditism of these animals, the position of their genital 

 organs, the complication and armature of their stomach, and the 

 purple liquid effused by several of their species, approximate them to 

 the Aplysiae. The shell, of such as have any, is more or less convo- 

 luted, but with little obliquity, and is without a projecting spire, 

 emargination, 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 

 thickness of the mantle, BULL^EA (a). It has but very few whorls, 

 and the animal is much too large to be drawn into it. 



Bullaa aperta, Lam.; Bulla apertaand Lobaria quadriloba, 

 Gm. ; Phyline quadripartite Ascan. ; Mull., Zool. Dan., JJI, pi. 

 ci. ; Blanc., Conch. Mm. Not., pi. xi ; Cuv., Ann. du Mus. t. I, 

 pi. xii, 6f. (The Sea Wafer), 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 occu- 

 pied by the shell, seem to divide its upper surface into four 

 lobes. Its thin, white, semi-diaphanous shell, is nearly all aper- 

 ture, and its gizzard is armed with three very thick rhomboidal 



* Bunatetta Lcachii, Blainv.,Malac., pi. xliii, f. 6. 



N.B. Authors hare also approximated to the Aplysiee the Apl. riridis, Montag., 

 Lin. Trans., VII, pi. vii, which forms the genus ACTION of Oken, and which is at 

 least closely allied to the Elysie timid f, Risso, Hist. Nat. Her., IV, pi. i, f. 3, 4 ; 

 as I am not acquainted with the branchiae of either, I cannot class them. 



f The Sonnet, Adans., Senegal, pi. i, f. 1, is a species closely allied to Bullaa; 

 but T cannot establish a genus, or even a species, upon so imperfect a document. 



0^7* (a) There are other reasons than those above-mentioned for the measure 

 employed by Lamarck. The shell of Bulla Aperta is not only slightly concave, but it 

 is very thin and fragile, and partially rolled inwards on itself. Indeed we may adduce 

 Lamarck's division of the Linntean genus bulla as a very happy specimen of the vast 

 superiority of the natural over the artificial system, for up to the time at which he 

 separated it into Bulliaea, Ovula, Physa, Terebellnm, and Achatina, and adding the 

 remainder of Bulla to the genera Pysuln, and Bulimus, the Linnaean genus was a 

 combination of the most discordant elements. Such as marine, fresh water, and 

 land shells. ENO. ED. 



