164 



of a shell, being but a very thin yellow transparent car- 

 tilaginous substance, of an ovate form, concealed within 

 the thicknessof the fleshy shield which covers the bran- 

 chiae, and which is attached to the posterior end of the 

 animal's back, by a point only at one side. 

 Aplysia depilans Aplysia fasciata 



Aplysia punctata. 



DOLABELLA. 



BULLA DUBIA. Of ' SOTtie AutllOTf. 



Encycl. Meth. pi. 83, /, 1,8. 

 Sowerby's Genera, No. 16, plate 6. 



This extraordinarily formed shell, like the Aplysia, (to 

 which it is closely allied, differing only in the substance 

 of the shell), is but the partial covering of a mol- 

 luscous animal: it is difficult of description, not pos- 

 sessing any of the common characters which distin- 

 guish other shells. Lamarck and Cuvier consider it 

 altogether an internal shell, and describe it as being of 

 rather an oblong form, a little arched in the shape of an 

 adze, one side narrower, thicker, more callous, and 



