I 



163 MANUAL OF THE MOLLUSCA. ( 



peculiar mode of development of their shells — if tlie observations upon Clau- I 

 silia and Helix may be extended to the rest. The first development of the i 

 shell \^dthin the substance of the mantle (a relation found hitherto only in the I 

 Cephalopoda) is up to the present time a solitary fact, without parallel among j 

 the other gasteropodous families." {Huxley) • 



FAMILY I. Helicid^.* Land-snails. i 



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

 animal ; aperture closed by an epipkragm during hybernation.f j 



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 vdih. a homy, dentated, crescent-shaped upper man- 

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

 ous, similar. (See Intr. p. ^7.) 



Helix, L.:|; 



Tijpe, H. pomatia, L. Roman snail. Eti/m. Helix, a coil. 



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

 pressed or conoidal ; apertiu-e 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. 



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

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

 and southward to Tierra-del-fuego, but most abundant by far in warm and 1 

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

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

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

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

 snail {fl. aspersa), have been naturalised in the most remote colonies. The i 

 Neapolitans and Brazilians eat snails. i 



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



Sections; Acavus, Montf. Shell imperforate. H. hsemastoma, PI. XII. 



fig 1. 



Geotrochus (lonchostoma) Hasselt, Trochiform, flat beneath. 



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



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

 Heliceoriim. ' 



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

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



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



