142 DEVONIAN FAUNA. 



2. PLEURONECTITES LEPIS, n. sp. Plate XVI, figs. 12, 13. 



Description. Left valve small, flat, circular, slightly transverse. Umbo low, 

 flat, direct, central, acute, small. Hinge-line apparently about half the length. 

 Anterior wing small, flat, triangular, rather narrow, denned by a strong, long, 

 rather concave wall from the umbo. Posterior wing very small, short, undefined. 

 Anterior margin rather concave at the wing, then sloping obliquely forward, and 

 becoming broadly convex round the body of the shell. Inferior margin wide, 

 gently convex. Posterior margin deeply convex below, becoming nearly straight 

 and oblique round the posterior wing. Contour of back nearly flat, perpendicular 

 and steep over the front wing. Surface marked by one or two strong growth- 

 lines, and apparently with very fine and regular concentric stride. Right valve very 

 similar to the left valve. 



Size. Height 15 mm., length 18 mm., depth of one valve 2 mm. 



Localities. Two, or perhaps three, specimens from Top Orchard are in the 

 Barnstaple Athena3um ; and one from Pilton in the Porter Collection. 



Remarks. It is not very certain whether this is a good species. The flattish 

 circular shape and general character appear to give a distinctive appearance ; but 

 in a deposit which has suffered so much from distortion it is exceedingly 

 difficult to decide whether an apparent peculiarity of shape may not possibly be 

 due to accident. It appears, however, that there is sufficient reason to assume 

 that it is distinct. 



Affinities. It seems rather similar to Aviculopecten Schulzi, Freeh, 1 in shape and 

 in the smoothness of the valves, but it differs by having a less defined and angu- 

 lated posterior wing. The wings in the German species, moreover, of which a 

 right valve only is figured, are strongly radiated. 



Streblopteria pullus, de Koninck, 2 appears more equilateral, and has a more 

 defined hind wing. 



3. PLEURONECTITES HICKSII, n. sp. Plate XVI, figs. 14, 14 a. 



Description. Left valve very small, convex, subcircular, higher than long. 

 Umbo low, sharp, direct, incurved, and extending somewhat above the hinge-line. 

 Hinge-line more than half the length of the shell. Anterior wing (probably 

 short) broad, triangular, defined by a straight, steep, oblique line from the umbo. 



1 1891, Freeh, Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 21, pi. i, fig. 10. 



2 1885, de Koninck, 'Ann. Mus. Eoy. H. N. Belg.,' vol. xi, p. 208, pi. xxxii, fig. 13. 



