222 GASTEROPODA OF THE INFERIOR OOLITE. 



159. Nerin^ea {Ptygmatis) Stroudiensis, WitcheU, 1887. Plate XVI, figs. 2 a, 2 h. 

 1887. Neeik^a Stboudiensis, Wiichell. Vol. cit., p. 83, pi. i, fig. 9. 



Description : 



Spiral angle (slightly obtuse) . . . 8°, 



Height of whorl to width . . . 1 : 1'4. 



liength of full-sized specimen . . .85 mm. 



Shell cylindro-conical, turrited, scarcely dimorphous. Whorls about twenty-five, 

 short and excavated towards the apex, and with a very thick sutural prominence. 

 Lower down the whorls become almost flat and angular, increasing by steps. In 

 some cases the anterior whorls are themselves slightly excavated. Traces of spiral 

 ornament are observable in the earlier whorls (see enlargement of fig. 2 h). The 

 section shows seven folds on the Oppelensis type. 



Relations and Distrihution. — Rather more conical than Ptyg. Oppelensis^ this 

 species further differs in the step-like character of the anterior whorls. Ptygmatis 

 velox, as we have seen, varies from Ptyg. Oppelensis in an opposite direction. Inter- 

 nally all three are closely related, and some might be disposed to regard them as 

 varieties of one species. 



Rare in the marly Limestone of Swift's Hill and Longridge. 



This terminates the Oppelensis-gronp. 



IGO. Nerintea (Ptygmatis) Cotteswoldij;, Lycett, 1857. Plate XVI, figs. 3 a — d, and 



var. CONICA, WitcheU,^gs. 4 

 a, b, and ? 4 c, d. 



1857. NERiNiEA CoTTESAVOLDiiE, Lycett. Cotteswold Hills, p. 124, pi. ii, fig. 2. 



Description : 



Spiral angle (regular) . . . 10''.^ 



Height of whorl to width . . . 1 : 1*75. 



Full length .... 80—100 mm. 



Shell cyHndro-conical, slightly dimorphous, apex acute. "Whorls from twenty 

 to twenty-five, extremely short and flat, except towards the apex, where a few of 

 the earher whorls exhibit considerable sutural prominence, but there is much 

 variety in this respect. The anterior whorls are flat or only very slightly 

 excavated, and there is httle or no prominence at the sutures, beyond traces of a 



> The spiral angle varies considerably, and is usually below 10° in specimens from the Lincolnshire 

 Limestone. 



