232 Lamarck's Genera of Shells. 



very slightly elevated ; aperture the whole length of the shell ; 

 right margin acute. 



The bulla differs from the bullsea, by the shell being com- 

 pletely convolute, alvvays visible externally, and only partially 

 covered by the hinder part of the animal, which adheres to it 

 by a muscular attachment. The animal even hides com- 

 pletely in the shell. In the buUaea the shell is imper- 

 fectly convolute, wholly concealed by the posterior part of the 

 mantle, but not affixed to it, and not at all visible externally. 



The genus bulla of Linnaeus was very vague and incon- 

 veniently extensive, as is evident from his B. ovum, achatinOf 

 Jicus, terebellum, &c., shells which belong to very different 

 genera and even families. Brugui^re reformed the genus, and 

 distinguished it clearly from the ovules, but be left the hullcea in 

 it, which Lamarck has since separated. The bullae are gene- 

 rally ventricose shells. 



Type. Bulla lignar'm*. (Idem. Linn.) 



Shell oblong, loosely convolute, attenuated towards the 



spire, transversely striated, pale yellow ; spire truncated ; 



ujnbiUcated. European Seas. PI. VII. Fig. 123. 11 Species, 



6th Family. 



Laplysiana. (2 Genera.) 



Branchiae placed in an appropriate cavity, near the posterior 

 part of the back, and covered by an opercular scutcheon. 

 Tentacula. 



The Laplysiana resemble large limaces, but iheir body is 

 broader, and larger towards the posterior part, and the borders 

 of the mantle are more ample. The head projects considerably 

 forward, and has four tentacula, two near the mouth, and two 

 behind. The latter are the largest, nearly ear-shaped, or 

 sometimes semi-tubular. They are distinguished from the 

 bullteana by the opercular scutcheon which covers the branchial 

 cavity, which, as well as the tentacula, is wanting in that 

 family. Thia scutcheon contains a horny or cretaceous piece, 

 the element of a shell, which has never the singular convolu- 

 tion of that of the bulla, or bullsea. The laplysiana breathe 



only water. 



* Belonging to wood. 



