68 CLASS III]. GASTEROPODA. ORDER VI. PULMOBRANCHIATA. 
the flat discoidal varieties, wherein the periphery of the outer whorl is 
sharp and angular, to Carocolla; those in which the last whorl is turned 
upwards, so that the aperture rests upon the penultimate whorl, on a plane 
with the spire, to Anostoma ; those of a narrow cylindrical form to Pupa ; 
those of a similar form, but provided with a shelly appendage for closing 
the aperture, to Clausilia ; those of an ovate or turriculated growth, with 
the columella simple, to Bulimus ; and those of the same form, with the 
columella truncated, to Achatina,—there still remains a numerous assem- 
blage of globose or conoidal varieties to the genus under consideration, 
We have before remarked, that there is no certain limit to any generic 
distribution ; and in this instance there are intermediate species of Helix 
or Carocolla, Pupa or Clausilia, Bulimus or Achatina, and so on, that may 
be referred with equal propriety to either. The ingenuity of the naturalist 
may thus be tried in every part of the system; what end then does it 
serve to overcharge the nomenclature with such genera as Omalonyz, 
Streptaxis, Polydontes, Pleurodonta, Dentellaria, Iberus, Chilotrema, Odon- 
tostylus, Tapada, Macrospira, Epistylium, Mesomphyx, Proserpina, Delom- 
phalus, Hyalina, Abida, Siphonostoma, Acavus, Polygyra, Geotrochus, Zo- 
mites, Gibbus, Cionella, and a host of others, all of which might be re- 
garded as good sectional divisions ? 
The shell of Helix may be described as being globose, orbicular, supe- 
riorly convex or conoidal, smooth, seldom striated, and generally covered 
with an epidermis ; the spire is rather obtuse, but little elevated, and the 
last whorl, which is more prominent, and has the circumference convex, 
forms a more or less distinct umbilicus ; the aperture is transverse, entire, 
and sometimes dentated within; the margins are disjoined, and the lip is 
either simple or reflected. 
The Helices, which are more or less distributed throughout the globe, 
have extraordinary powers of vitality; after being shut up in a torpid 
state for years, they have been known to crawl forth in full animation 
upon being placed upon a fresh green leaf. They have also a peculiar 
mode of hibernating or retiring into a state of torpidity: in the absence 
of an operculum the animal covers the mouth of its shell with an irregular 
layer of mucus, which, when hardened, forms a thin calcareous lid called 
