128 DEVONIAN FAUNA. 



Description. — Right valve large, probably nearly circular, flattisb, with small, 

 nearly equal, and well-defined wings. Umbo nearly central, acute, depressed, proxi- 

 mate, not elevated above the hinge-line. Front wing flat, narrow, with an oblique 

 convex margin, meeting the hinge-line at right angles, and defined below by a 

 deep, oblique sinus. Posterior wing narrow, triangular, with a concave margin, 

 meeting the hinge-line at right angles, and defined below by a less definite sinus. 

 Anterior margin deeply notched under the wing, produced centrally, and broadly 

 and evenly convex. Inferior and posterior margins convex. Surface of back 

 ornamented by numerous sharp, triangular rays (divided by deep linear furrows) 

 which are simple near the umbo, but, as they recede from it, develop a smaller 

 similar ray on each side, so that near the margins they form groups of three 

 triangular ridges, of which the central is the highest ; the whole surface being 

 crossed by numerous regular, fine, sharp, distant threads or strise. Surface of 

 front wing with four or five strong, rounded ridges, divided by similar furrows, 

 crossed by numerous fine, rounded strias. Surface of hind wing with more 

 numerous and indistinct rays, crossed by rather more irregular strias. 



Left valve very similar, but probably rather deeper, and with a larger, broader, 

 and less defined hind wing. 



Size. — Phillips's figured specimen is 51 mm. long, but is vertically compressed. 

 Other specimens are still larger, but I have been unable to find any that give the 

 true dimensions, all the specimens having suffered distortion. 



Localities. — In the Museum of Practical Geology is Phillips's figured specimen 

 from Brushford, and a second from Braunton. In the Barnstaple Athenasum are 

 two fine specimens from Goodleigh and Pilland, and a poor one from Top Orchard ; 

 in the Porter Collection are two specimens from Pilton ; and in the Woodwardian 

 Museum are five specimens from Barnstaple and one from South Petherwyn. 



Remarks. — Though always distorted, several of the specimens are very fine, 

 and enable us to learn a good deal of the character of the shell. 



Phillips, though adopting Sowerby's name, remarks that he has very little 

 doubt that it is the same shell as Pterinea radiata, Goldfuss. 1 M'Coy, however, 

 points out that it is distinct from that species. It is distinguished by its radiated 

 wings, and its more numerous and finer ribs of nearly equal size, grouped with 

 remarkable regularity in a different way from those of the German form, which, 

 moreover, has wider interspaces. 



1 1834-40, Goldfuss, ' Petref. Germ./ vol. ii, p. 135, pi. cxix, figs. 7a, b; and ? 1891, Freeh, 

 ' Abhandl. Geol. Specialk. Preuss.,' Baud ix, pt. 3, p. 19, pi. i, fig. 2. 



