10 PULMONATA. 



(Liranffiidse) occur in the English Wealden, hut fossil land-snails 

 have not been found in strata older than the tertiary in Europe, 

 and then under forms generically, and even in one instance spe- 

 cificall}^, identical with living types of the New World (Mega- 

 spira, Proserpina, Glandina, and Helix labj^rinthica). — Woodward. 



The oldest American fossils of this subclass occur in the 

 Carboniferous. 



The lingual dentition of the Pulmonata confirms, in a remark- 

 able manner, those views respecting the affinities of the subclass, 

 and its zoological value, which have been deduced from the more 

 obvious characters afforded by the animal and shell. They have, 

 without known exception, rows of ver}^ numerous, similar teeth, 

 with broad bases, resembling tessellated pavement. Their crowns 

 are recurved, and either aculeate or dentated. The lingual ribbon 

 is very broad, often nearl}^ as wide as it is long ; and the number of 

 teeth in a row (though usually a third less) is sometimes as great, 

 or even greater, than the number of rows. The rows of teeth are 

 straight or curved or angulated ; when the rows are straight the 

 teeth are similar in shape ; curves indicate gradual changes, and 

 angles accompany sudden alterations of form. — Woodward. 



The jaw is single, or is composed of three pieces, never of two 

 pieces as in the branchiferous snails. 



In the 3' oung snails the temporary vellum is rudimentary or 

 absent, with the exception of the maritime genei-a, in which it is 

 well-developed. The first development of the shell, at least in 

 Limax, Clausilia and Helix, is within, instead of on the exterior 

 surface of the mantle as in the other gastropods. It is similar 

 in most cephalopods, but in these the shell continues internal, 

 whilst in most of the pulmoniferous genera it becomes external 

 at an early period. 



The Pulmonata are conveniently divided into the orders : — 



1. Stylommatophora (Geophila, Ads. Nephropneusta, Iher- 

 ing). — Eyes at the ends of the superior tentacles. 



2. Basommatophora (Branehiopneusta, Ihering\ — Eyes at the 

 base of the tentacles. 



Order STYLOMMATOPHOKA. 



Terrestrial mollusks having four tentacles, the superior pair 

 invaginate or retractile, oculiferous at their extremities. They 

 may be divided into Monotremata and Ditremata, according to 

 the union or separation of the sexual openings. 



Suborder MONOTREMATA. 



Male and female orifices united ; oculiferous tentacles invertible. 



* Agnatha. Mouth without jaw ; generally no median tooth 

 in the radula ; lips often developed into feeler-like appendages ; 

 neck commonly elongated, and peculiarly furrowed on the back. 



