﻿200 DEVONIAN FAUNA. 



2. Plattostoma ? deforme, Sowerhy sp. PI. XXIII, figs. 1 — 5. 



1840. Nerita depormis, Sowe?-by. Geol. Trans., ser. 2, vol. v, pt. 3, pi. lvii, fig. 14. 



1845. — spirata, Sowerby. Ency. Metrop., p. 578. 



1854. — deformis, Morris. Cat. Brit. Foss., p. 264. 



1889. — — Whidborne. Geol. Mag., dec. 3, vol. vi, p. 30. 



Description. — Shell rather small, subglobose, spirally conical, of two or three 

 volutions. Spire, small, very rapidly increasing, excentric, irregularly coiled. 

 Suture deep, acute. Whorls irregularly convex, more or less elevated above the 

 lower suture; flattened on the basal side, but becoming gradually rounder as 

 they advance from the apex. Body-whorl transversely flattened at first, gradually 

 expanding, so as to become very large and capacious near the mouth ; sometimes 

 spirally compressed along its centre, so as almost to form a blunt angle or 

 undeveloped keel. Mouth very large, subcircular, entire. Lips discontinuous. 

 Inner lip replaced for one-third part by the parietal wall. Peristome sharp, 

 bevelled all round. Columella very long, slightly arching and slightly twisted. 

 Umbilicus small and very deep. Shell-structure apparently rather thin. Surface 

 ornamented by very fine, regular, and numerous striae, arching convexly very 

 rapidly backwards from the suture, but becoming concave and perpendicular upon 

 the centre of the whorl and towards the base of the shell. 



Size. — A middle-sized specimen measures 14 mm. in height by 13 mm. in 

 width. A large specimen is 22 mm. wide. 



Localities. — From Wolborough there are five specimens in Mr. Vicary's 

 Collection; nine, or perhaps ten, in the Godwin-Austen Collection in the Museum 

 of Practical Geology ; two in the British Museum ; and seven 1 in the Torquay 

 Museum. From Lummaton there is a small specimen in the Woodwardian 

 Museum. 



Remarks. — This species appears to be decidedly common at Wolborough. As 

 far as the state of the specimens will allow a judgment to be formed, it appears 

 to be a distinctly variable shell, especially in the height and shape of its spire. 

 In the young shell this seems to be almost flat, and scarcely indented by the 

 suture-lines, while in the more aged specimens it becomes elevated and sub- 

 turrited. 



The shape of the base of the shell also seems to change with its growth, that 

 of the upper whorls appearing to be flat, while that of the body-whorl gradually 

 becomes convex and produced in front. 



1 Only three of these seven specimens are certainly from Wolborough ; the others may be from 

 Lummaton. 



