271 



ndges, one of which overhangs and hides the margin. The 

 surface is more strongly reticulate than shown in the figure • 

 It has a low tubercle on the anterior third, and a limited 

 impression on the posterior region, near the dorsal border 

 Mge view, bluntly sub-sagittate ; end view, sub-quadrate. 

 Four examples; Blue Fullers-earth Clay, Midford. 



54. CYTHERIDEA OSTREATA,* sp. n, 



PI. iv., figs. 6 a, b, c. 

 A large and sub-oblong Cytheridea, obliquely rounded in front 

 contracted and irregularly angular behind. Dorsal mar-^in 

 straight; anterior hinge-angle prominent, hinder hinge-angle 

 hidden by a coarse, irregular growth of shelly matter. Surface 

 reticulate, with irregular meshes, looking like oyster-spat. Two 

 strong ridges runs along the ventral region, the upper of which 

 turns upwards, and runs parallel with the two ends of the valve 

 for some distance. Hingement, as in pi. i., fig. 2. 

 One specimen ; Yellow Fullers-earth Clay, Midford. 



55. CYTHERIDEA RUGIFERA, sp. n. 



PI. v., figs. 11 a, b, c. 



Oblong, obliquely rounded in front, rounded and deeply 

 rimmed behind. Upper and lower margins slightly incurved. 

 Surface rugulose (not well shown in the figure), with numerous 

 smaU, shallow, irregular depressions. A slight curved ridge 

 rises above and behind the front hinge. 



From the base of the Fullers-earth Oolite between Notgrove 

 and Bourton. In Mr. E. A. Walford's collection. 



56. CYTHERIDEA ACUTIPLICATA, n. sp. 



PI. iv., figs. 7 a, b; 8 a, b, c. 

 Obovate, bei ng ^roade r (higher) anter iorly than posteriorly. 



* Scabby, as if covered with small oyster shells. 



