64 Lamarck's Genera of Shel/s. 



Shell cylindrical, transversely striated : stria; dotted ; spire 

 nearly concealed in the folds of the shell, pointed ; base of the colu- 

 mella triplicate. Fossil, from Grignon. PI. v. Fig. 202. 5 Re- 

 cent species, and 1 fossil. 



5th Family. 

 Convoluta. (6 genera.) 



No canal ; base of the aperture notched, or effuse; whorls of the 

 spire wide, compressed, convolute, the last whorl almost entirely 

 covering the others. 



The convoluta constitute the last family of the trachelipoda. 

 Like the columellaria, their shell has no canal at the lower part, 

 but a notch at the base of the aperture. The most remarkable 

 thing in regard to their form, is the great width of the whorls, so 

 that the last almost wholly envelopes all the rest. Hence the 

 spiral cavity of the shell is long and narrow, and the body of the 

 animal must, consequently, be considerably flattened. 



The shells of the two first genera have the right lip of the aper- 

 ture curved inwards. 



1. Ovula*. 



Shell inflated, attenuated or subacuminated at each end ; lips 

 curved inwards. Aperture longitudinal, narrow, effuse at the ex- 

 tremities ; left lip not indented. 



Linneus confounded the ovulae with his bulls, from which they 

 were first distinguished by Bruguieres. They are closely allied to 

 the cypraese, in point of form ; are sometimes rostrated at both 

 ends, nearly smooth, and have no spire. They are distinguished 

 from the cyprsea;, by the left lip never having any indentations, and 

 from the bullae, by the turning inwards of the right lip. 



The shells of this genus never have a lamina resting onthecolu- 

 mellar lip, which is always naked, smooth, and more or less in- 

 flated. They have neither epidermis nor operculum. 



Type. Ovula oviformis't. (Bulla ovum. Linn.) 



* Dim. from ovum, an egg. 



t Egg-shaped. Lamarck divides the species into two sections, viz., those 

 with the right lip plicated, and those in which it is smooth. 



