170 Proceedings of the Royal Pliysical Society. 



deeply ; mouth irregularly oval, longer than wide ; outer lip 

 sharp and erect ; inner lip thickened, and reflected over the 

 body whirl to form a more or less developed, elongated cal- 

 losity, without platings or other markings. Surface usually 

 plain, but in some specimens finely striated over the whole 

 surface, especially that of the last, or body whirl. Umbilicus, 

 no distinct trace. 



Qls. — This little shell, of which the largest specimens before 

 me measure about three and a quarter lines in length, has 

 many points in common with a much larger species of the 

 genus, Naticopsis plicistria (Phillips),* with the type speci- 

 mens of which I have carefully compared it. So much so is 

 this the case, that I hesitate to apply to the present shell a 

 distinctive name, although the two forms are in all proba- 

 bility distinct, and it is difficult to consider one which does 

 not increase beyond the size mentioned above, so far as the 

 specimens show, identical with one assuming gigantic propor- 

 tions in comparison, an average size of iV. plicistria being one 

 inch seven lines long. 



The two shells resemble one another in the great dispro- 

 portion of the body whirl to the others, it being in each case 

 many times larger, in the shoulder-like form of the upper 

 part of the body whirl, in the deep channelled condition of 

 the sutures, and in the form of the mouth. On the other 

 hand, they differ in the great inequality of the size, in the 

 generally more oblique form of iV. plicistria, in the more 

 pronounced and larger spire of the Fifeness specimens in 

 proportion to the total size of the entire shell in each case, 

 and in the absence on the columellar lip of the latter of the 

 oblique strise or ridges seen in JSf. plicistria. 



It will be better to avoid giving this shell any definite 

 name at present, but in the event of its proving distinct both 

 from N. plicistria and the other described forms of N'aticopsis, 

 it may perhaps be called JSF. communis. 



Loc. and Horizon. — Shore near Fifeness, N.E. coast of Fife ; 

 in the Calciferous Sandstone or Lower Carboniferous series — 

 Coll. Geol. Survey, Scotland, and Mus. Pract. Geol., collected 

 by the late Mr E. Gibbs. 



* Geol. Yorkshire, p. 225, t. 14, f. 25. 



