﻿ORTHONYCIIIA. 223 



2. Orthonychia quadrangularis, n. sp. PI. XXI, figs. 8, 8 a, 8 b. 



P 1878. Capulus? sp., Kayser. Abbandl. Geol. Specialk. Preuss., Baud ii.pt. 4, 



p. 98, pi. xvii, figs. 1, 1 a. 



Description. — Shell large, rather elevated, conical or campanulate, without 

 volutions. Apical extremity horizontally compressed, erect or very slightly recurved, 

 gently bent upwards, not spiral. Apex itself accidentally removed in type 

 specimen. Perpendicular from apex falling within the aperture, but very near 

 its front. Mouth very large, oval or oblong, considerably wider than long. 

 Margins sinuous, consisting of eight or nine double undulations, which are 

 strongest at the front or outer part of the peristome. Shape of shell rather 

 elongate at apex, then very rapidly expanding for about a third of its height, and 

 there turning through a blunt elbow and proceeding in a slightly expanding cone 

 to the aperture, gradually developing the undulations seen at the mouth. Surface 

 covered with low, subsinuous, irregular growth-ridges, which are seen under a 

 lens to be composed of very fine, discontinuous, fimbriated lines. Shell-structure 

 extremely thin, almost papyraceous. Mould (?) marked on the back by numerous 

 straight, definite, longitudinal ridges, and a few concentric bulges, corresponding 

 with the chief growth-lines of the shell. 



Size. — Height from apex 21 (probably 22) mm., length of mouth 28 mm., 

 width of mouth 38 mm. 



Localities. — There is a fine specimen in the Torquay Museum, which may have 

 come from Wolborough ; and a smaller specimen in my Collection, which came 

 from Lummaton. 



Remarks. — This fine shell seems to be distinguished by its untwisted elevated 

 apex, gently undulating surface, and peculiar bell-shaped form. 



Affinities. — This species comes very near to Platyceras (Orthonychia) conicum, 

 Hall. 1 That shell seems to be extremely variable, but differences may be observed 

 in the greater flatness and convexity, and in the more lateral position of the apex 

 of the English form. 



It comes very near to Orthonychia costata, Barrois, with which at first I 

 regarded it as identical, but the presence on the latter of a number of sharp, 

 radiating ridges seems to indicate that they are specifically distinct. 



In Capulus hercynicus, Kayser, 3 the perpendicular from the apex to the plane of 

 the mouth is very much longer, and, except in the varieties where it is longest, 



1 1879, Hall, 'Pal. N. T.,' vol. v, pt. 2, p. 3, pi. i, figs. 13-23. 



2 1878, Kayser, ' Abhaudl. Geol. Specialk. Preuss.,' Baud ii, pt. 4, p. 89, pi. xiv, figs. 1—14. 



