334 GASTEROPODA OF THE INFERIOR OOLITE. 



Bibliography, Sfc. — This species or variety was first noticed by Phillips, who 

 referred it to the Nerita costata of the ' Mineral Conchology.' D'Orbigny re-named 

 it iV". pseudo-costata, and by that name this rather abundant Dogger shell has gene- 

 rally been known to British palaeontologists. Not quoted in the ' Terrains Juras- 

 siques.' 



Description. — The width and height are nearly equal, the height of a full-sized 

 specimen being about 9 mm. In other respects the shape of the shell as in the 

 preceding species. The flanks of all the whorls are ornamented with very strong 

 radial costaa, regular, and separated by sulci about twice the width of each rib. 



Relations and Distribution. — This form can be regarded as little more than a 

 variety of the preceding species, somewhat less transverse in shape, and with 

 stouter and fewer ribs. It replaces N. costulata in the Yorkshire Dogger, and occurs 

 very sparingly in the Pea-grit of Crickley. It is not improbable that Nerita 

 costifera, Piette, from the Bathonian of Rumigny, is a micromorph of this species 

 on a higher horizon. 



267. Nerita subrugosa, sp. nov. Plate XL, figs. 7 a, 7 b, 8. 



Description : 



Height .... 8 mm. 



Width .... 93 mm. 



Shell transversely ovate, angulated, rather higher than wide, thick ; spire short, 

 few-whorled, whorls sunk in a deep channel. Body- whorl relatively large, flattened 

 and angulated posteriorly, and provided with a carina of moderate salience, 

 which is situated rather above the middle of the whorl. Costse fine, regular, and 

 numerous, and exhibiting slight nodes on crossing the median carina. Aperture 

 very wide, columellar area flattened ; other indications wanting. 



Relations and Distribution. — Nerita subrugosa is a form intermediate between 

 Nerita costulata, Desh., and Nerita rugosa, Morris and Lycett. From the former it 

 differs in its more angular outline, in the development of a median carina, and in 

 the finer and more closely-set costse. 



The specimen figured (Plate XXVIII, fig. 6) in the present work, from the 

 Scarborough Limestone, probably represents a sort of a passage between N. cos- 

 tulata and N. subrugosa, where there is a very slight tendency to a median carina. 

 On the other hand, Nerita rugosa, M. and L., is less transversely ovate, has a higher 

 spire, and the median carina is much more strongly developed ; it is in fact 

 altogether a coarser shell. 



Nerita subrugosa has been found sparingly in the Scarborough Limestone at 



