PTERIA. 59 



But the niiinl)ei' of those ribs A-aries considerably, and our specimens agree per- 

 fectly with the figures given by Waagen. The specimens from Faringdon are 

 smaller than those found in the Speeton Clay, and they present some resemblance 

 to P. pediiuda (see beloAv), Ijut the presence of several smaller ribs in the inter- 

 spaces connects them with /'. Corniieliana. 



Types. — From the Hils-thon of Elligser Brink. The specimen from Upwarc 

 figured hy Keeping is in the Sedgwick ]\Iuseuni ; it is imperfectly preserved, but is 

 probably an example of this species. 



Dlstrihidion. — Speeton Clay (zone of Bclemnites lateralis, D 1) of Speeton. 

 Claxby Ironstone (zone of B. hifcralis) of Claxby. Tealby Clay (zone of B.jacnlum) 

 of Claxby. Lower Greensand of Faringdon. Gault of Folkestone.' 



Pteeia (Oxytoma) fectinata (Snirrrbi/), 1830. Plate VIII, figs. 8a, I>, 0, 10,,,/,, 



11-1:3, Ua, h. 



1836. AvicuLA PECTiNATA, J. de C. Soirerby. Tiuns. Geol. Soc, ser. 2, vol. iv, iip. 



128, 338, pi. xiv. fig. 3. 

 1854. — — /. Morris. Cat. Brit. Foss., ed. 2, p. 163. 



1869. — — F.J. Pidet and G. Campiche. Foss. Terr. Crct. Ste. 



Croix (Mati'r. Pal. Suisse, ser. 5), 



p. 70. 



Nou 1846. — —A. d'Orhljinj. Pal. Fraiu'. Terr. Crut., vol. iii, p. 473, 



pi. cccxci, figs. 1 — 3. 



s 



JJcscii'iiiidn. — Shell small, obli(jueIy oval, with evenly rouiuled margin. Height 

 a little greater than length. 



Left valve convex, ornamented with luimerous slender ribs often having sharp 

 sunnnits. Frequently the ribs are of two sizes — larger and smaller, alternating in 

 a more or less regular manner. But in some cases the ribs near the margin of the 

 valve are of equal or nearly equal size. The interspaces are flattened and con- 

 siderably broader than the ribs. Anterior ear moderatel}' large, triangular, the 

 outer angle nearly- a right angle ; surface with ribs similar to those on the rest of 

 the valve. Posterior ear much longer than the anterior, wing-like, with concave 

 growth-lines; on the dorsal part a few slender ribs occur but are often indistinct 

 or absent near the valve. 



Right valve moderately convex dorsally, flattened ventrally, surface smooth or 

 wdth very fine radial and concentric ribs. Posterior ear large, not distinctly limited. 

 Anterior ear small. 



' The only specimen seen from this horizon is in the British Museum, No. L. 16,880. 



