PTERINOPECTEN. 135 



It appears referable to the genus Pterinopecten. The front wing is very 

 definite, and the adjacent front boundary of the back is long, straight, and deep ; 

 the hind wing is more diffuse and broad. The transverse threads are so delicate 

 that they are only occasionally visible or preserved. The ribs are rather irregular, 

 a few being larger than the rest; toward the rear they become smaller and more 

 even, and then, as a rule, suddenly cease, the last rib reaching the margin above the 

 postero-inferior corner. The space behind this seems smooth, but is really 

 covered with microscopic rays, and upon it the transverse threads become very 

 prominent. 



Affinities. From Pecten alternatus, Phillips, 1 it differs by its smaller and more 

 numerous ribs, and by its sharp transverse threads. The latter character may, 

 however, perhaps only be due to a better state of preservation ; and the former is 

 weakened by the fact that while our specimens have usually about thirty rays, in 

 one case they are reduced to twenty. Phillips gives the number as about twelve 

 and represents them as very much larger, closer, and rounder ; so that there seems 

 sufficient reason to regard his species as distinct. 



Aviculopecten (Pterinopecten) dauniensis, Freeh, 2 approximates it, but is more 

 oblique, with a smaller umbo, larger wings, and decidedly fewer and coarser rays 

 and concentric ridges. 



3. PTERINOPECTEN SCABKIRADIANS, n. sp. Plate XV, figs. 8, 9; and Plate XVII, 



fig. 4. 



Description. Eight valve small, flat. Umbo small, apparently central, not 

 elevated above the hinge-line. Hinge-line probably as long as the shell. Front wing 

 very long, deeply notched, and extremely narrow, with a long, very oblique, slightly 

 sigmoid margin, and separated from the body by a straight, deep, oblique groove. 

 Lower margins apparently convex. Hind wing undefined. Surface bearing 

 rather numerous, close, strong, rounded, highly nodulated rays, which frequently 

 divaricate, and are separated by linear furrows, sometimes perhaps crossed by 

 undulations. Surface of front wing with two very strong nodulated rays near the 

 hinge, and smooth below. 



? Left valve very convex, subcircular. Umbo acute, elevated above the hinge. 

 Hind wing large, very broad, triangular, flat, bounded by a straight margin, and 

 rather well defined by a line from the umbo to the margin. Lower margin 

 apparently almost evenly convex. Surface covered by about twenty very distant, 

 narrow, elevated, sharpish rays, crossed by and nodulated by still more distant, 

 regular, parallel, concentric lines, enclosing with the rays flat oblong interspaces. 



1 1841, Phillips, ' Pal. Foss.,' p. 47, pi. xxi, fig. 78. 



2 1891, Freeh, 'Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 22, pi. i, figs. 8 81. 



