222 GASTEROPODA OF THE INFERIOR OOLITE. 
159. Nerinaa (Ptygmatis) Srroupiensis, Witchell, 1887. Plate XVI, figs. 2 a, 2 b. 
1887. Nerinwa Srrovuptensis, Witchell. Vol. cit., p. 33, pl. 1, fig. 9. 
Description : 
Spiral angle (slightly obtuse). ; o Or. 
Height of whorl to width ' : » fee aleae 
Length of full-sized specimen. . 85 mm. 
Shell cylindro-conical, turrited, scarcely diaovahena 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. 2b). The 
section shows seven folds on the Oppelensis type. 
Relations and Distribution.—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-group. 
160. Nerina (Ptygmatis) Correswotpim, Lycett, 1857. Plate XVI, figs. 3 a—d, and 
var. oonrIcA, Witchell, figs. 4 
a, b, and P4c, d. 
1857. Nertnma Correswoipra, Lycett. Cotteswold Hills, p. 124, pl. ii, fig. 2. 
Description : 
Spiral angle (regular) : cealirse 
Height of whorl to width . ; woralesdle7! 
Full length : : . 80—100 mm. 
Shell cylindro-conical, slightly damlanpnduay apex acute. Whorls from twenty 
to twenty-five, extremely short and flat, except towards the apex, where a few of 
the earlier 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 little or no prominence at the sutures, beyond traces of a 
1 The spiral angle varies considerably, and is usually below 10° in specimens from the Lincolnshire 
Limestone. 
