166 Proceedings of the Royal Physical Society. 



these localities may be allowed to remain as one and the 

 same. 



In the globular form, depressed spire, ventricose body 

 whirl, and thick reflected inner lip these shells more or less 

 resemble the genus Ampullaria ; or so far as the form is 

 concerned, they are not unlike some Neritinm. If, however, 

 our shells possess an umbilicus they cannot be referable to 

 either of these genera, to say nothing of the internal absorp- 

 tion seen in Neritina, and of which we here know nothing, or 

 of the denticulated inner lip of the latter genus, which is cer- 

 tainly not present in our little fossils. 



The globular few-whirled form and small spire equally 

 relate them to Natica as to Ampullaria, and they further 

 agree with the former in the callous inner lip, covering and 

 obliterating the umbilicus, if it existed. There is, however, 

 a group of Palaeozoic shells, British and North American, 

 consisting of the genera Naticopsis (M'Coy), Platyostoma 

 (Conrad), and Strophostylus^ (Hall), all closely united, with 

 many characters in common, so that it is at times difficult to 

 separate them, but still, when a series of individuals are col- 

 lected, it is at once seen that they distribute themselves in 

 these groups, more or less separated by distinctive characters. 

 The abbreviated descriptions of these genera, taken from their 

 respective authors, are as follows : 



Genus Naticopsis (M'Coy, 1844). — Globose elliptical shells, 

 with a small spire of few convex whirls ; a large, broad, ovate 

 aperture, rounded in front. The columella is thick, callous, 

 flattened, and either plain or obliquely striated. (?) Umbilicus 

 present and small. Operculum concentric, and non-spiral. 



Genus Platyostoma (Conrad). — Globose shells with low 

 spires; aperture very large, sub-orbicular, and dilated. 

 Outer and inner, or columellar lip, thickened and reflected ; 

 last volution, or whirl, much expanded. 



Genus Strophostylus (Hall, 1879).* — Sub- (or ovoid) globose 

 shells with low spires, and a large ventricose body whirl; 

 aperture round-ovate, or transversely broad-oval; outer lip 

 * Pal., N. York, iii., p. 303. 



