NERIN^A. 
225 
spire is sub-turrited or step-like. Lower down tins feature disappears, and the 
whorls succeed each other without any prominence, except that, in well-preserved 
specimens, a slight posterior marginal rim may be noted on one or two of the 
latest whorls. Lines of growth may be observed in the later whorls of such a 
specimen as fig. 8 a, otherwise no traces of ornament have been discovered. 
The aperture is subrhomboidal, and, as in the case of Ptyg, Goiteswoldisd, bears 
no trace of the presence of folds when the shell is complete (fig. 8 a). On the 
other hand, when the shell is fragmentary (fig. 8 h) the aperture exhibits three 
folds on the columella, and one on the outer wall. The section shows five folds in 
all, two on the outer wall and three on the columellar side, of which the upper one 
may be regarded as being in the posterior wall. These folds are large and 
complex, and must have reduced the available space, the result being a whimsical 
figure. 
Relations and Distribution. — Ptygmatis Santonis belongs to the Cotteswoldise- 
group, but differs in the absence of the fourth fold on the columellar side. It is 
also narrower than the majority of specimens of Ptyg. Gotteswoldix, and the 
whorls are relatively higher. It may possibly represent N. triplicata, Voltz. 
based on the cast of a Ptygmatis too imperfectly diagnosed to be accepted as a 
species. 
Occurs in the Lincolnshire Limestone at Santon, and very rarely in the marly 
Oolite of Longridge. 
163. Nerin^a {Ptygmatis) brbvivoluta, sp. nov. Plate XVI, figs. 9 a, 9 &, and ? 10. 
Description : 
Spiral angle (regular) .... 12° — 14°. 
Height of whorl to width . . . 1 : 2'2. 
Length . . , , .35 mm. 
Shell conical, slightly turrited, apex acute. Whorls about twenty-one, 
extremely short. In the apical region the sutural belts are thick and prominent, 
in the later whorls they are well defined but thinner, and the whorls themselves 
are slightly excavated. No trace of ornamentation has hitherto been noted. 
Body-whorl short and angular ; aperture angular and more wide than high ; 
canal but little reflexed. The section shows five folds, two on the outer wall, 
three on the columellar side. Owing to the large size and complex nature of 
three of these folds (fig. 9 h), the interior space was very much restricted. The 
anterior fold on the outer wall might sometimes be construed as two folds. 
Relations and Distribution. — Ptyg. brevivoluta belongs to the Gottesivoldige-grouip, 
29 
