134 DEVONIAN FAUNA. 



Myalinodonta Normaniana, d'Orbigny, sp., 1 as given by (Ehlert, 2 differs 

 specifically in the absence of major ribs, as well as generically in the absence of an 

 anterior wing 



Aviculopecten transversus is easily distinguished by its obliquity being less, 

 and by its ribs being piled up in groups. 



2. Pterinopecten ? Hallii, n. sp. Plate XV, figs. 2—6. 



P1887. Aviculopecteit, cf. exacuttts, Tschemyscliew. Mem. Com. Geol., vol. iii, 



pt. 3, p. 45, pi. vii, fig. 7. 



Description. — Left valve small, convex, subcircular, not oblique. Umbo large, 

 rounded, rather prominent, subcentral, subacute, proximate, and slightly elevated 

 above the hinge-line. Anterior wing rather large, broad, triangular, slightly 

 convex, sharply defined, with a convex margin meeting the hinge-line at about 

 100°. Posterior wing large, broad, triangular, undefined, with a concave margin 

 meeting the hinge-line at an acute angle of about 60°. Hinge-line straight, nearly 

 or fully equal to the length of the shell. Contour of back highly and evenly convex, 

 perpendicular by the anterior, and rather steep by the posterior wing. Anterior 

 margin long, convex round the wing, sharply concave at its base, and then broadly 

 convex round the lower part. Inferior margin roundly and evenly convex. 

 Posterior margin broad, sigmoid, nearly vertical. Surface of back covered (1) 

 except on the extreme posterior part, with twenty-five to forty prominent, elevated, 

 rounded, alternating, radiating ribs, becoming smaller rearward, and diminishing 

 in number as they approach the umbo, and (2) on the extreme posterior part by a 

 number of microscopic rays ; the whole crossed by twenty or thirty minute, sharp, 

 regular, parallel, very distant threads. Surface of wings with five or six fine, 

 distant radiations, and with rather coarser and closer transverse striae. 



Size of left valve. — Length 15 mm., height 15 mm., depth 5 mm. 



Localities. — In the Barnstaple Athenaeum are four specimens from Top Orchard, 

 one from Meer Top, and one from Eoborongh. In the Porter Collection is one 

 from Pilton. 



Remarks. — These specimens, though fairly preserved, are all more or less 

 defective, especially about the wings, and all appear to be left valves. There is not, 

 therefore, material fully to describe the shell, and it is of course possible that right 

 valves described under another head really belong to it, though I do not at 

 present know of any which there is any reason to match with it. 



1 1849, d'Orbigny, « Prodrome,' vol. i, p. 87. 



2 1882, (Ehlert, ' Mem. Soc. Geol. Fr.,' ser. 3, vol. ii, p. 30, pi. v, figs. 1—1 e. 



