﻿222 DEVONIAN FAUNA. 



2. Sub-genus. — Oethonychia, Hall, 1843. 



This is a sub-genus of Gapulus, which is to be distinguished by its rounded 

 mouth, the entire absence of a spire, and the straight or only very slightly 

 recurved apex, the perpendicular from which falls within the circle of the mouth. 



It is rare in Devonshire, and I am only acquainted with three specimens 

 representing two species, but on the Continent and in America it seems to be 

 sufficiently abundant. It occurs in the Devonian and Carboniferous formations. 



1. Orthontchia costata, Barrois. PI. XXI, figs. 7,7 a, 7 b. 



1889. Plattceeas costatum, Barrois. Faun. Calc. d'Ebray, p. 196, pi. xiii, 



figs. 5, 5 a — c. 



Description. — Shell rather small, depressed, transversely conical or campanulate, 

 without a spire. Apex gone, but apical region horizontally compressed, slightly 

 bent upwards, situated slightly above the median horizontal line. Perpendicular 

 from apex falling well witbin the margin of the mouth. Sides of the shell 

 spreading out from near the apex to the mouth with a slightly convex curve, the 

 greatest convexity being along the back or outer side. Mouth large, flat, broadly 

 oval. Surface covered by irregular, microscopic, undulating growth-striae and 

 indistinct radiating lines, and also on the greater part of the marginal third of 

 the shell by a few strong, distant, sharpish, radiating ridges, visible to the 

 naked eye. 



Size. — Width 21 mm., breadth from apex to mouth 15 mm., height 18 mm. 



Locality. — There is a single specimen from Lummaton in Mr. Champernowne's 

 Collection. 



Remarks. — This species is distinguished by its simple cup-shaped form, by its 

 radiating ridges, which seem to vanish in the peristome, and by the absence of any 

 spire. The only other fossil at all like it from the localities now under review is 

 Orthonychia quadrangularis, but that shell is sufficiently distinguished by its less 

 elevated form and its almost flat surface. 



Barrois's figured specimen has rather more numerous costas than the English 

 specimen, and its apex is slightly more distant from the mouth, and more central 

 in respect to it, but on the whole there can be, I think, no doubt that it is 

 identical. 



