162 MANUAL OF THE MOLLUSCA. 



peculiar mode of development of their shells if the observations upon Clau- 

 silia 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.) 



FAMILY I. HELICULE.* Land-snails. 



Shell external, usually well developed, and capable of containing the entire 

 animal ; aperture closed by an epiphragm during hybernation.f 



Animal, with a short retractile head, with four cylindrical, retractile ten- 

 tacles, 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 man- 

 dible ; lingual membrane oblong, central teeth in- conspicuous, laterals numer- 

 ous, similar. (See Intr. p. 17.) 



HELIX, L. \ 



Type, H. pomatia, L. Roman snail. Etym. Helix, a coil. 



Shell umbilicated, perforated or imperforate; discoidal, globosely-de- 

 pressed 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. 



Distr. including the sub-genera, above 1,200 sp. (several hundred sp. are 

 undescribed). World- wide ; ranging northward as far as the limit of trees, 

 and southward to Tierra-del-fuego, but most abundant by far in warm and 

 humid climates. M. D'Orbigny observed 6 sp. at elevations exceeding 11,000 

 feet, in S. America, and Layard found H. gardeneri at the height of 8,000 

 feet in Ceylon. The species of tropical and southern islands are mostly 

 peculiar. Several of the smaller British species, and even the large garden- 

 snail (H. aspersa\ have been naturalised in the most remote colonies. The 

 Neapolitans and Brazilians eat snails. 



Fossil (extinct) sp. about 50. Eocene . Europe. 



Sections; Acavus, Montf. Shell imperforate. H. ha3mastoma, PL XII. 

 fig.L 



Geotrochus (lonchostoma) Hasselt, Trochiform, flat beneath. 



Polygyra, Say. Depressed, many- whirled. H. polygyrata, PI. XII. fig. 2. 



* The account of this family is chiefly taken from Dr. L. Pfeiffer's Monographia 

 Jfeliceorum. 



t The epiphragm is a layer of hardened mucus, sometimes strengthened with car- 

 bonate of lime ; it is always minutely perforated opposite the respiratory orifice. 



J The synonomy of the genus would fill several pages. See Intr. 1, p. 59. 



