﻿DEVONIAN FAUNA. 



Pterinea, sp., Kayser, 1 is more inequilateral and still less transverse. 

 In Lyriopecten orbicularis, Hall, 2 the ribs are coarser, and the front wing is 

 undefined. 



Avicnhi simjil/rirosta, Trenkner, 3 seems to have a smaller front wing and close 

 rounded rays divided by linear furrows. 



Aviculopecten coelatus, M'Coy, 4 which is a kindred Carboniferous form, is much 

 more coarsely ribbed. 



4. Genus. — Crenipecten, Hall, 1883. 



Hall defines this genus as having " the form of Aviculopecten, but with a hinge 

 furnished with a series of small cartilage-pits throughout its entire length." This 

 distinctive hinge is not visible in any of our English examples, but they so nearly 

 correspond with the shells placed by Hall in this group that they may presump- 

 tively be located within it. 



1. Crenipecten ? comma, Whidborne, sp. PI. X, figs. 4, 4 a, 5, 5 a. 



1889. Avictjlopecten comma, Whidborne. Geol. Mag., dec. 3, vol. vi, p. 79. 



Description. — Left valve small, flattish, triangular, equilateral, oblique. Umbo 

 small, sharp, central, direct, proximate, slightly elevated. Hinge-margin short, 

 straight. Front wing unseen. Hind wing small, short, flat, broad, triangular. 

 Sides of the umbo defined by two nearly straight steep declivities, forming the 

 boundaries of the shell apart from the wings, of which the front is about one- 

 third, and the rear about two-thirds the total breadth of the shell. Front 

 margin rather narrow, slightly concave as far as the end of the declivity, and 

 then becoming convex. Inferior margin obliquely convex. Posterior margin 

 oblique, straight for the greatest part of its width, and then produced and convex 

 in the inferior region. Contour of valve-surface gently convex, almost perpen- 

 dicular at the sides, and spreading out flatly to the ventral margins. Surface 

 covered with about thirty low, rounded, alternating ribs, separated by much 

 wider, flat interspaces ; some of the ribs reaching almost to the umbo, but others 

 being much smaller and starting much lower down ; the whole crossed by numerous, 

 very fine, linear, distant threads, which thus reticulate the surface. 



Size. — Length 9 mm., width 9 mm., depth of one valve 1 mm. 



1 187s, Kayser, ' Abhandl. Geol. Specialk. Preuss.,' Band ii, pt. 4, p. 135, pi. xix, fig. 5. 



2 1884, Hall, ' Pal. N. Y.,' vol. v, pt, 1, p. 42, pi. iv, figs. 3— S ; and pi. lxxxii, fig. 3. 

 ; L868, Trenkner, 1 Palaont. Novitat.,' pt. 2, p. 23, pi. vii, fig. 4. 



1 L855, M'Coy, ' Brit. Pal. Fobs.,' p. 483, pi. iii, figs. 5, 5 a. 



