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. 

 Oed. PULMONATA, Cuv. 



TERRICOLA, 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 



* Etym. "E\«£, quod contortum est. 



