

(i) 



(2) 



Length 



23 



22 



Height 1 



35 



33 



Thickness . 



26 



2(3 



(4) 



(5) 



14 . 



14 mm. 



20-5 . 



19 „ 



16 . 



15 „ 



OPIS. 119 



Posterior margin truncated, slightly concave, forming an angle with the gently 

 curved ventral margin and also with the postero-dorsal margin. Umbones 

 prominent, slender, greatly incurved, almost touching in the young, but separated 

 in older specimens. A prominent carina extends from the umbo to the postero- 

 ventral angle, cutting off an area which is divided into two parts by a prominent 

 but rounded carina which ends at the postero-dorsal angle ; the outer part only of 

 the area is seen in a side view, and is concave ; the inner part is depressed, and its 

 dorsal portion is flattened and resembles a lunule. Lunule very large, cordate, 

 flattened. 



Ornamentation consists of many small concentric ribs separated by narrow 

 grooves. Behind and in front of the flattened part of the valve this ornamentation 

 becomes less distinct or may disappear altogether. Margin of valve entire. 

 Measurements : 



C-i) 



20 



29 



24 



(1 — 5) Lower Greensand, Upware. 



Affinities. — This species shows some resemblance to 0. Hugardiana, d'Orbigny, 3 

 from the Gault. 



Remarks. — The shell is relatively higher in large than in small specimens. In 

 all the examples obtained from Upware the shell is preserved. Specimens from 

 Seend are in the Museum of Practical Geology. 



Types. — Leyinerie's specimen came from the Lower Neocomian of Bernon 

 (Aube). D'Orbigny's specimens were obtained from Saint Sauveur (Yonne), 

 Bernon, and Marolles. The specimen figured by Keeping is in the Sedgwick 

 Museum. 



Distribution. — Lower Greensand of Upware and Seend. Internal casts, 

 probably belonging to this species, are found in the Lower Greensand of Colesliill 

 near Faringdon. 



Oris iialdonensis, sp. nov. Plate XVIII, fig. 1 a-d. 



Description. — Shell trigonal, higher than long, moderately inequilateral, convex, 

 with flattened sides. Anterior margin slightly convex, passing gradually into the 



1 Measured from the umbo to the postero-ventral angle. 



2 Syn. 0. Sabaudiana, d'Orbigny, 'Pal. Franc. Terr. Cret.,' vol. iii (1844), p. 53, pi. eclvii, figs. 

 4—6 ; Pictet and Eoux, ' Moll. Foss. Gres verts de Geneve' (1852), pp. 432—434, pi. xxxii, fig. 1. 



