GREY CHALK MARL. Ill 



It shews the plicated folds of the columella, and the broad band of the 

 outer Up. 



Fig. 3. A smooth cast, in which the spire is more produced than usual. 



Fig. 34. A large specimen, exhibiting the back of the shell. 



Tab. xviii. fig. 3. is a distorted cast, that bears a closer affinity to 

 Auricula simulata of Sowerby, {Min. Conch, tab. 163, figs. 5. 8.) than to 

 the present species. 



Locahties. Hamsey, Middleham, Stoneham, Offham. 



23. Ampullaria? Tab. xviii. fig. 11. 



The cast of a subglobose, ventricose, univalve, probably belonging to 

 the genus Ampullaria : — the depressions of the spire, and the obUque form 

 of the cast, originate from compression. 



Locality. Hamsey. 



24. Vermicularia umbonata. Tab. xviii. fig. 24. 



Discoidal, spire depressed, concave beneath, umbonated above ; the 

 outer volution produced, and marked with distant, annular ridges. 



This species is commonly about 0-7 inch in diameter, and consists of 

 two or three volutions. It is slightly concave, or umbihcated, on its in- 

 ferior surface, the inner whorls of the upper sides being concealed by 

 an umbo. The produced part frequently exceeds in length the longest 

 diameter of the shell, and is marked with sharp annular ridges ; where 

 these occvu', the substance of the shell is much thickened, the cavity of 

 the tube being diminished nearly one-third. The aperture is simple, and 

 round. 



Fig. 24. This example shows the depressed spire with its central 

 obtuse knob, and a considerable portion of the produced part of the 

 external volution. In every specimen of this fossil the shell, hardened 

 by an impregnation of calcareous spar, still remains. 



Locality. Hamsey. 



25. Vermicularia Sowerhii. Tab. xviii. figs. 14, t5. 



Conical, spiral, smooth, umbiHcate, inner wreaths anchylosed, slightly 

 inserted ; aperture indented by the preceding volution ; outer whorl not 

 produced ? 



