BULLA. GASTEROPODA. 63 
of the world. The genus is very comprehensive, and may be divided into the 
following sections : — 
Section 1. Body large, and destitute of an umbilicus. Example, Helix 
aspersda. 
Section 2. Body large, provided with an umbilicus at the base. 
Section 3. Body large, outer lip thickened, and provided with teeth. 
Example, Helix nux denticulata. 
Section 4. Body very large, carinated ; spine short, conical, and depressed. 
Example, Helix lapicida. Caracolla lapicida, of Lamarck. 
The Baron De Ferussac has united the following genera under the generic 
name Helix, namely, Helix, Bulinus, Clausilia, Achatina, Anastoma, Lapicida, 
Azeca, &c. These he has again formed into sub-genera. 
Genus LXXXIV. — STROPHOS TOMA. — Deshayes. 
GenericeCharacter. — Shell pyramidal, depressed ; body 
very large; spire very small, consisting of few rapidly 
diminishing volutions ; base of body nearly flat, with a 
carinated margin, and provided with.a pretty large and deep 
umbilicus ; aperture sublunate, and obliquely turned up- 
wards towards the spire ; lips entire; provided with an 
operculum. 
Strophostoma ferussina. Plate VI. fig. 25. 
This is exclusively a fossil genus, and closely connected with Anostoma, but 
is distinguished from that genus by being umbilicated. 
ORDER V.—GASTEROPODA. 
Animals with the body straight, never spiral, nor totally 
enveloped in their shell ; the foot or disc situated under the 
belly, and united to the body nearly its whole length, and 
serving as an organ of locomotion. 
GRAND-DIVISION I. —PNEUMOBRANCHIA. 
Branchie in the form of a vascular net, on the wall of a particular cavity, 
opening by a hole which the animal contracts or dilates at pleasure. They 
respire air. 
TRIBE I.—BULLACEA. 
Shells greatly distended, and without any apparent colu- 
mella. 
