PTEEIA. 50 



But the number of tliose ribs varies considerably, and our specimens agree per- 

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

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

 to /'. pectinate (see below), but the presence of several smaller ribs in the inter- 

 spaces connects them with P. Comueliana. 



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

 figured by Keeping is in the Sedgwick Museum ; it is imperfectly preserved, but is 

 probably an example of this species. 



Distribution- Speeton Clay (zone of Belemnites lateralis, D 1) of Speeton. 

 Claxby Ironstone (zone of B. lateralis) of Claxby. Tealby Clay (zone of B.jacuhim) 

 of Claxby. Lower Greenland of Faringdon. Gault of Folkestone. 1 



Pteeia (Oxytoma) pecttnata {Sowerby), 1836. Plate VIII, figs. 8a, b, 9, 10a, &, 



11-13, 14 ft, 6. 



1836. Avicula pectinata, .7. (lc C. Sowerby. Trans. Geol. Soc, ser. 2, vol. iv, pp. 



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

 1854. /. Morris. Cat. Brit. Poss., ed. 2, p. 163. 



1869. F. J. Pictet and G. Campiche. Fuss. Terr. Cret. Ste. 



Croix (Mater. Pal. Suisse, ser. 5), 



p. 70. 



Non 1846. A. d'Orbigny. Pal. Franc. Terr. Cret., vol. iii, p. 473, 



pi. cccxci, figs. 1 — 3. 



Description. — Shell small, obliquely oval, with evenly rounded margin. Height 

 a little greater than length. 



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

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

 a more or less regular manner. But in some eases 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 moderately 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 vent rally, surface smooth or 

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

 Anterior ear small. 



1 The only specimen seen from this horizon is in (lie British Museum, No. L. 16,880. 



