﻿LYRIOPECTEN. 



87 



triangular, flat, well defined. Posterior wing large, undefined. Anterior margin 

 very broad, sigmoid, being concave on the wing and then advancing and becoming 

 regularly convex over its greatest portion. Inferior margin apparently moderately 

 convex. Posterior margin apparently moderately convex below, and becoming 

 slightly concave near the hinge-margin. Contour of surface slightly convex in 

 the central parts, divided from the front wing by a straight, perpendicular 

 declivity from the umbo, and becoming slightly concave longitudinally in the 

 postero-superior margin, so as to form the hind wing. Surface marked by 

 multitudinous, fine, alternating and rather irregularly placed, narrow, elevated 

 rays, divided by broader concave interspaces, and crossed by equally numerous, 

 very fine, distant threads, so as to divide the surface into hollow tesseras. Shell- 

 structure papyraceous. Right valve unknown. 



Size. — Length 44 mm., width 45 mm., depth of one valve 7 mm. 



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

 Lummaton. 



Remarks. — This is a very beautiful and distinct species. Mr. Champernowne's 

 fine fossil is unfortunately much injured round the margin, so that the shape can 

 only be made out approximately by tracing the lines of growth ; the surface, 

 moreover, is slightly decayed, so that the fine reticulations can only be observed 

 in occasional patches. 



The shell is widely distinct from any that accompany it, and may easily be 

 distinguished by its broad wings, by the central position and small obliquity of its 

 umbo, and by the very great fineness of its ornamentation. 



Affinities. — Phillips's figure 1 of Pecten transversus, Sowerby, 2 presents some 

 similarity. Specimens of that shell, however, in Mr. Townsend Hall's Collection 

 and in the Museum of Practical Geology show that it is very different. For 

 instance, its ornament is coarser, and consists of sharp triangular ridges grouped 

 in sets of three, the central of which is the largest. Sowerby's original description 

 bears out its distinctness ; while Pterinea radiata, Goldfuss, 3 with which Mr. 

 Phillips identifies the North-Devon shell, is still further removed from ours, 

 having very much fewer and more rounded ribs. 



Pecten lineatus, Goldfuss, 4 is more oblique, and has still more numerous and 

 closer ribs. That shell seems very kindred to P. granulosus, Phillips. 5 



Orhipecten Follmanni, Freeh, 6 approaches it most nearly, but is distinguished by 

 a less defined front wing, and the absence of the prominent transverse threads. 



1 1841, Phillips, ' Pal. Foss.,' p. 10. pi. xxi, figs. 7, 7 a, b. 



2 1840, Sowerby, ' Geo!. Trans.,' ser. 2, vol. v, pt. 3, pi. liii, fig. 3. 



3 1834-40, Goldfuss, ' Petref. Germ.,' vol. li, p. 128, pi. cxix, figs. 7 a, b. 

 1 Ibid., p. 78, pi. cxiv, fig. 9. 



5 1841, Phillips, 'Pal. Foss.,.' p. 46, pi. xxi, figs. 75a— c. 



fi 1891, Freeh, ' Abhandl. Geol. Specialk. Preuss.,' Baud ix, pt. 3, p. 29, pi. ii, figs. 8—9 a. 



