A92 MOLLUSCA SUB-KINGDOM VI 
Order 2. PULMONATA. Cuvier. Air-breathing Snails.! 
Euthyneura in which the gill cavity is transformed into a lung for breathing free arr. 
Mainly terrestrial or fresh-water forms. 
A few Pulmonates have reverted to exclusively aquatic habits, and have the lung 
filled with water; and in a few, secondary gills are developed in the cavity. These, 
however, are rare exceptions. The great majority of forms breathe air by means of a 
network of blood-vessels spread upon the inner surface of the lung. The ordinary 
aquatic forms come to the surface of the water at intervals to renew their supply of 
air. They have, with few exceptions, no operculum, and the shell is often vestigeal or 
absent. 
Next to the Prosobranchs the Pulmonates are the largest group of Gastropods, 
there being upwards of 6000 living and 700 fossil species known. The most 
important and highly diversified genera (Helix, Bulimus, Clausilia) are terrestrial in 
habit ; certain others (Planorbis, Limnaea, Physa) are confined to fresh water. The 
oldest Pulmonates are of rare occurrence in the Devonian and Carboniferous ; they 
are found sparingly in the Jura and Cretaceous, are of greater abundance in the 
Tertiary, but do not attain their maximum distribution until the present geological 
period. 
The Thalassophila and Auriculidae are restricted to marine deposits; remaining 
Pulmonates are rarely found outside of fresh-water strata, and are commonly associated 
with other fresh-water organisms that have been swept by rainfall or running water 
into swamps or estuaries. 
Sub-Order A. THALASSOPHILA. Gray. 
Shell either spiral and operculate, or bowl-shaped to depressed conical, without spire, 
and somewhat unsymmetrical. Animal usually provided with a single gill in addition 
to the lung cavity. Tentacles fused with the discoidal head. Eyes sessile. 
The Thalassophila inhabit the littoral zone of the ocean and brackish estuaries. Fossil 
remains occur from the Devonian onward. Three families are recognised —Siphonari- 
idae, Gadiniidae, and Am- 
phibolidae; but these are 
not readily distinguishable 
by shell characters alone. 
Stphonaria, Blainville 
(Fig. 1027). Shell usually 
radially ribbed. Apex 
directed backwards or to- 
ward theleftside; internally 
with two unequal muscular 

Fic. 1028. impressions, which are in- 
pal Hercynella bohemica, Barr. De- terrupted on the right side 
Siphonaria crassicostata, Desh. vonian (Ktage F); Lochkow, ;., ¢, oat ‘nad frooyv 
Eocene; Anvers, near Paris. Bohemia. in front by a broad Sroove. 
Tertiary and Recent. 
Hercynella, Kayser (Fig. 1028). Devonian. <Anisomyon, Meek and Hayden. Jura 
and Cretaceous. 
Valenciennesia, Rousseau. Shell very thin, broadly bowl-shaped, concentrically 
ribbed. Apex situated near the posterior margin. Right side bearing a broad 
1 Sandberger, F., Land- und Siisswasser-Conchylien der Vorwelt. 1879-75. 
White, C. A., Review of American non-marine Mollusca. 
Tryon, G. W. and Pilsbry, H. A., Manual of Conchology, Pulmonata. 
