692 MR. F. CHAPMAN ON THE BARG ATE BEDS OF SURREY. [Nov. 1 894, 



18. Cytheropteron laticristatum (Bosquet). 



Cyihere laticristata, Bosquet, Mem. Comm. Carte geol. Neerlande 

 vol. ii. (1854) p. 108, pi. vii. figs. 11 a-d. 



This species appears to form a link between C. sphenoides 

 (Beuss) and 0. alatum (Bosquet), the postero-ventral wing of the 

 above species showing an intermediate stage of development. 

 Bosquet obtained his specimens from Upper Cretaceous and Tertiary 

 beds. 



A very perfect and typical valve from clay of Pebble-beds, 

 Littleton. 



19. Cytheropteron reticulosttm, sp. nov. (PI. XXXIII. fig. 6 a, 



b,c.) 



Yalve subrhomboidal, with well-rounded anterior, and somewhat 

 oblique and slightly beaked posterior margin. The postero-ventral 

 process rises more anteriorly than in C. umbonatum (Will.) 1 , and is 

 less prominent. The area between this alar process and the antero- 

 dorsal margin is marked with interrupted surface-reticulations. 

 Length of valve -^ in. ("45 mm.). 



One valve from clay of Pebble-beds, Littleton. 



20. Cttheropteron costtjliferum, sp. nov. (PL XXXIII. fig. 7 a, 

 b, c.) 



Side view of carapace, subovate, narrow, and rounded in front, 

 but bluntly pointed behind. Valve thickest at one-third from the 

 posterior end, sloping towards the antero-dorsal margins, and 

 highest in the middle of the dorsal edge. The ventral face is nearly 

 flat, hollowed slightly towards the ventral margins of the valves. 

 Dorsal margin bordered with a flange which continues less strongly 

 along the ventral margin. The ventral aspect shows the test- 

 surface striated longitudinally with about four low and narrow 

 costulae on each valve ; and the surface of the carapace also has 

 several weak longitudinal ridges on each valve. The postero-ventral 

 swelling resembles that of C. concentricum, var. virginea, Jones. 

 Length of valve Jg- in. (0-45 mm.). 



Two valves in conjunction, from clay-seams of Pebble-beds, 

 Littleton. 



Of the twenty species and varieties just enumerated, seven are 

 apparently new ; nine have been previously noticed from Cretaceous 

 strata generally, whilst four are undoubted Jurassic forms. 



1 Mon. Cret. Entom. Suppl., Pal. Soc. (1890) p. 40, pi. i. figs. 21-26. 



