288 MANUAL OF THE MOLLUSCA. 
tached to the parietes of the ‘ vitellary’ vesicle, which Gegenbaur 
and Schmidt compare to a Wolffian body. 
‘‘Gegenbaur draws attention to the fact, that the first rudi- 
ment of the-shell in Limaw, Clausilia, and probably Heliw, is not 
secreted on the exterior of the mantle, as in other gasteropoda ; 
but.is deposited, in the form of calcareous granules, within its 
substance. 
‘‘ Besides, therefore, the possession of Wolffian bodies, and of 
especial contractile organs, which subserve respiration and cir- 
culation during embryonic life—-the terrestrial gasteropoda are 
further distinguished by the peculiar mode of development of 
their shells—if the observations upon Clausilia and Helix may 
be extended to the rest. The first development of the shell 
within the substance of the mantle (a relation found hitherto 
only in the Cephalopoda) is up to the present time a solitary 
fact, without parallel among the other gasteropodous families.” 
(Huxley.) | 
FAmMiIty I.—HELIcIpm.* I[Land-snails. 
Shell external, usually well developed, and capable of con- 
taining the entire animal; aperture closed by an epiphragm 
during hybernation.t 
Animal with a short retractile head, with four cylindrical, 
retractile tentacles, the upper pair longest and bearing eye- 
specks at their summits. Body spiral, distinct from the foot; 
respiratory orifice on the right side, beneath the margin of the 
shell; reproductive orifice near the base of the right ocular 
tentacle ; mouth armed with a horny, dentated, crescent-shaped 
upper mandible; lingual membrane oblong, central teeth in- 
conspicuous, laterals numerous, similar. 
lehoinoy 1bes 
Type, H. pomatia, L., Roman snail. 
Etymology, Helix, a coil. 
Shell umbilicated, perforated or imperforate; discoidal, 
globosely-depressed or conoidal; aperture transverse, oblique, 
lunar, or roundish; margins distinct, remote, or united by 
callus. 
Animal with a long foot, pointed behind ; lingual teeth usually 
in straight rows, edge-teeth dentated. 
* The account of this family is chiefly taken from Dr. L. Pfeiffer’s Monographia 
Heliceorum. 
{ The epiphragm is a layer of hardened mucus, sometimes strengthened with car. 
bonate of lime; it is always minutely perforated opposite the respiratory orifice. 
~ The synonomy of the genus would fill several pages. See p. 48, 
