85 
LIY. Volvaria. A cylindrical convoluted univalve : the spire not 
extruded : the opening narrow, the length of the shell : the colu- 
mella plicated at its base. 
This shell, for Lamarck knows but of one species, V. bulloides, which 
is fossil, approaches very near to Bulla cylindrica, or Bulla solida ; 
but differs from the genus Bulla, in having its columella plicated. 
LY. Ampullaria. A ventricose subglobose univalve, with an um- 
bilicated base : the opening oblong and entire, with no thickening 
on the left lip. 
Th e Ampullaria is a river shell of the warm climates. Its spire, which 
always projects a little, distinguishes this genus from Planorhis ; and 
there being no thickening on the left lip, distinguishes it from Natica. 
Ampullaria patula, Lam. is Helix mutahilis, Brand, Foss. 5 1 /. Tab. 
iv. In Brander’s figure the back is only seen; and the patulous 
opening, the specific characteristic, is not shown. A. sigaretina, 
Lam. differs from the preceding, chiefly in having no umbilicus. 
From the greatest part of these shells, answering to the preceding 
description, being marine shells, and somewhat approaching in cha- 
racter to the genus Natica, Lamarck is disposed to think that they 
belong to a genus not yet established. Twelve species appear to 
exist among the fossils of the environs of Paris : A. pygmcea , A. exca- 
vata, A. conica, A. acuta, A. acuminata, A. spirata, A. depressa, A. canal- 
iculata, A. patula, A. sigaretina, A. crassatina, A. hybrida. 
A. spirata, I find among my Veronese fossils ; and A. conica, and 
a shell much resembling A. rugosa, I have found among the shells of 
the Essex cliff. 
LYI. Planorhis. A discoidal univalve. The spire depressed, 
hardly at all prominent, the turns conspicuous on both sides. The 
opening entire and oblong ; the margin never reflected. 
The shells of this genus are fresh-water shells : their inferior face 
is known, by its being more sunk in than the upper ; and from the 
gradual diminution of the turns towards the centre, forming a funnel- 
formed cavity. 
