A MONOGRAPH 



OF THE 



MOLLUSCA FROM THE CRAG. 



CLASS CEPHALOPODA. 



No remains of any animal belonging to this Class have, that I am aware of, been 

 detected in any of the three Formations into which the Crag is divided. My cabinet 

 contains a few specimens of Belemnites belonging to two different species, found by 

 myself among the gravelly portion of the Red Crag. These, however, as they have 

 been introduced from the older rocks, and have no connexion with the Tertiary 

 Periods, do not require to be here particularised. 



CLASS GASTEROPODA. 



ORD. PULMONATA, Cuv. 



TERHICOLA, FLEM. 



HELIX,* Linn. 1758. 



Generic Character. Shell turbinated, orbicular, subglobose or depressed, light 

 and thin : spire slightly elevated, with several more or less convex volutions, mostly 

 smooth ; last whorl often large and ventricose, with an oblique aperture of a lunate or 

 semi-ovate form, generally broader than long, impressed by the prominent part of 

 the body whorl : peristome confluent with the columella, mostly strengthened 

 internally by a thickened rib, and often having a reflected edge, especially on the left 

 side covering the umbilicus, without an operculum. 



Animals belonging to this order (Pulmonata), differ from the generality of the 

 Gasteropoda in being capable of respiration direct from the atmosphere, and are fur- 



* Etym. "EXt, quod contortum est. 



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