14 MOLLUSCA FROM THE GREAT OOLITE. 



which is cited by that author as occurring both in the Great and Inferior Oolite of 

 Normandy. We also possess the same species from the Inferior Oolite of Bridport and 

 Gloucestershire. It differs, however, essentially from the original specimen of Am. discus, 

 Sow., described in the ' Min. Conch.,' tab. 12, which has a more regular, sagittate aperture, 

 and does not possess the central flattened space, so characteristic of our species. 



Locality. Great Oolite of Minchinhampton, Lycett. In the same formation at 

 Ranville (Calvados), Niort (Deux Sevres), Mansigny (Vendee), D'Orbiyny. In the Inferior 

 Oolite at Bridport, and near Stroud; Eterville and Moutiers (Calvados). 



We have much pleasure in assigning to this species the name of G. R. Waterhouse, 

 Esq., whose arrangement and careful study of the Cephalopoda, contained in the National 

 Collection, have materially assisted this branch of Palaeontology. 



Class — Gasteropoda. Cuvier. 

 Order— Prosobranchi ata. M. Edwards. 



Ctenobranchiata, Schweigger. 



Family — Strombid^e. 



Pterocera, Lamarck, 1801. 



Shell turrited, ventricose, spire usually short, aperture oval, having a lengthened canal at 

 both extremities, outer lip expanded into hollow thickened spines, with an anterior sinus 

 separate from the caudal canal. 



Pterocera ignobilis. Plate III, fig. 14. 



P. Testa parvd turbinatd; spird breviusculd; anfractibus Iceviyatis, planatis (3 — 4) ultimo 

 obsolete transversim bicarinato ; carina superiori obsolete nodosa; caudd brevi. 



Shell small, turbinated, spire short, whorls smooth, flattened (3 — 4), the last whorl twice 

 carinated, the upper carina obscurely nodulous, canal short. 



The great breadth of the whorls, and the obscurely bicarinated last whorl, are the leading 

 features. This shell approaches Alaria laviyata; but in that species the spire is much more 

 lengthened, and the volutions do not become angular, until at least five have been com- 

 pleted, it then produces small processes, which are deciduous, and the last whorl does not 

 attain any undue magnitude ; but, in the species before us, the fourth volution is large, has 

 considerable squareness, but with scarcely any distinct carina. 



Locality. Rare in the planking of Minchinhampton Common. 



