PTERINOPECTEN. 137 



anteriorly, direct and extending slightly above the hinge-margin. Hinge-margin 

 giving the greatest length of the shell, straight behind the umbo, and at rather a 

 lower level and slightly oblique in front of it. Anterior wing rather small, broad, 

 triangular, flat, denned by a depression running obliquely forward from the apex, 

 and marked by two or three linear rays, and by eight or nine sharp, distant, 

 regular, transverse ridges. Hind wing large, flat, broad, undefined. Anterior 

 margin nearly straight and perpendicular above, and becoming obliquely rounded 

 in the lower part, the curve continuing along the inferior margin, and the postero- 

 inferior corner being roundly convex. Posterior margin perpendicular and 

 slightly concave. Surface covered with about eighteen strong, steep, acute, 

 triangular, elevated, very distant ribs, becoming stronger and more distant 

 gradually from the rear forwards, and separated by broad, gently convex 

 intervals ; the whole crossed by thirteen or fourteen sharp, regular and regularly 

 distant threads or subfoliaceous ridges, which are slightly concave between the 

 rays. Rays produced into long marginal spines, so that the margin is, in the 

 central parts at least, deeply scalloped. Lateral angles sharp and slightly acute. 



Size of Valve. Height 22 mm., length 23 mm., depth about 4 mm. 



Localities. There are four specimens of the left valve from Pilton in 

 Mr. Porter's Collection, and one from Barnstaple in the Woodwardian Museum. 

 Romer found a specimen in the " first quarry nortli of Pilton on the way to 

 Marwood." 



Remarks. This species was long ago founded by F. A. Romer on a Devonshire 

 fossil, but it appears to have escaped the notice of English geologists, as I can 

 find no reference to it in either Morris's or Etheridge's Catalogue, or elsewhere. 

 Not having seen Romer' s type specimen, I had intended to quote it simply on his 

 authority ; but in Mr. Porter's Collection I at once recognised four examples of it, 

 one of which is almost perfect, and agrees in every respect with Romer's figure 

 and description. He remarks that the concentric ribs are strongest on the swollen 

 intervals, while they become small and form no clear knots upon the rays. The 

 species is far removed from any other English Devonian species, and from any 

 foreign species described by Freeh, Hall, &c. 



5. PTEKINOPECTEN MUNDUS, n. sp. Plate XV, figs. 12, 12 a, 13, 13 a. 



Description. Shell large, oblique, convex. Left valve more or less convex, 

 very oblique. Anterior wing small, narrow. Umbo minute, not elevated above 

 the umbo. Hinge-line straight (in front of umbo), lined with three or four 

 minute, parallel, transverse cartilage-furrows. Anterior margin short, convex, 



