PBRNOPECTEN. 143 



Posterior wing apparently obtusely triangular, small. Lower margins probably 

 strongly convex. Contour very gently convex, becoming perpendicular or even 

 rather excavate above the lines which bound the wings. Surface microscopically 

 marked by crowded, regular, elevated, distant concentric threads, and similar but 

 less regular and distinct radiating lines, and with a few transverse strias on the 

 front wing. 



Size. — The specimens are too defective for measurement. 



Localities. — A specimen from Bradford is in the Barnstaple Athenseum ; and a 

 very doubtful one from Pilton in the Porter Collection. One from the lane 

 between Wrafton and Heanton, and another from Upcott Arch Quarry, are in my 

 Collection. 



Remarks. — This is another little species, of the nature of which we have at 

 present very imperfect information. There seems no doubt that it is quite distin- 

 guishable from PI. Piltonensis, but I am not so certain whether PI. lepis may not 

 prove to be a synonym of it. The fine concentric ornament is very characteristic, 

 and appears to be different from that on the adjacent species. 



Affinities. — The right valve of Pecten perobliquns, F. A. Romer, 1 comes very 

 near, but seems to differ in being shorter and much more oblique. 



Pleuronectites devonicus, Freeh, 2 is closely approximate, with an exactly similar 

 ornament, but having a smaller and radiated front wing and a rounder umbo. 

 Its front wing seems nearer an equilateral triangle in shape, and the front margin 

 is consequently more indented. It also appears to be a more globose shell. 



3. Genus — Pernopecten, Winchell, 1865. 



This genus is regarded by Zittel as a section of Crenipecten. Hall 3 refers to it 

 the Palaeozoic (if not also the Jurassic) species of Entolium, Meek ; and shows that, 

 if identical, it has a priority of a few months over the latter. 



Its hinge-line is described as straight, but in the type specimen as figured by 

 Hall the wings protrude upward at least as much as in the shell described below. 



1. Pernopecten insperatus, n. sp. Plate XVII, fig. 5. 



Description. — Shell small, flat, nearly equilateral, subcircular ; umbo flat, low, 

 slightly anterior, small, rounded. Wings subequal, protruding to a moderate height 



1 1850, F. A. Komer, ' Beitr. Harzgeb.,' pt. i, p. 48, pi. viii, fig. 4. 



2 1891, Freeh, ' Abhandl. G-eol. Specialk. Preuss.,' Band ix, pt. 3, p. 13, pi. xvii, figs. 8, 8 a. 



3 1885, Hall, ' Pal. N. T.,' vol. v, pt. 1, sect, ii, p. lvii, woodcuts 1—3. 



