MOLLUSUA. GASTEROPODA 245 



with a long straight or .slightly curved anterior canal, and a 

 posterior canal applied to the spire ; outer lip expanded, with 

 tooth-like processes, and an anterior notch. Operculum small, 

 oval or claw-shaped, edge not serrated. Eocene to present day. 

 Ex. R. curta, Recent ; R. lucida, London Clay, etc. 



Hippochrenes. Similar to Rostdlaria, but outer lip wing- 

 like and without processes. Upper Cretaceous and Eocene. Ex. 

 H. amplus, Barton Beds. 



Rimella. Similar to Rostellaria, but with cancellate orna- 

 mentation ; outer lip but little expanded and reflected outwards ; 

 canal reaching nearly to the apex of the spire. Eocene to present 

 day. Ex. R. rimosa, Barton Beds. 



CypraBa. Shell ovoid or elongate, convex, convolute, surface 

 covered with shining enamel. Spire almost or quite concealed by 

 the last whorl. Aperture oblong and narrow, as long as the shell, 

 with a short canal at each end ; outer lip inflected and crenulated ; 

 inner lip crenulated. In the young form the outer lip is thin and 

 the spire prominent. Eocene to present day. Ex. C. mappa, 

 Recent ; C. oviformis, London Clay. Trivia is similar but smaller 

 and with transverse ribs. Eocene to present day. Ex. T. europcea, 

 Recent. 



Tritonium (fig. 98). Shell thick, oval or fusiform. Spire 

 elongate, with varices which are continued over a few whorls only. 

 Aperture with a posterior notch, and a slightly curved anterior 

 canal ; outer lip thick, crenulate internally ; inner lip with callus 

 and usually with folds. Cretaceous to present day. Ex. T. varie- 

 gatum, Recent ; T. nodulosum, Barton and Bracklesham Beds. 



Buccinum. Shell oval or elongate, without an umbilicus. 

 Spire of moderate length. Whorls ventricose, smooth or with 

 longitudinal folds. Aperture oval, large ; outer lip simple, thin ; 

 anterior canal short, truncated, a little reflected ; columella a little 

 sinuous. Operculum small, oval or circular. Eocene to present 

 day. Ex. B. undatum, Coralline Crag to present day. 



Nassa. Shell solid, ovate, elongate without umbilicus, 

 usually ornamented. Aperture oval, with a very short re- 

 flected anterior canal ; inner lip with callus, reflected on to the 

 last whorl, with a ridge near the posterior end ; outer lip thick, 



