THE TERTIARY FORMATION. 55 



Var. I. Plate V, fig. 18. 



? Cytiierella Beyrichi, Bornemann. [? Cytherina Beyrichi, Reuss.] Zeitsch. Deutsch. geol. 



Ges., vii, p. 354, t. 20, fig. 1 . 



INCH. 



Length, 7 ' 5 Lower Eocene : London. 



Carapace sub-quadrangular ; extremities rounded and more or less denticulate : 

 valves depressed anteriorly, convex behind; marked with a strong uniform punctation. 

 Dorsal profile narrow-acute-ovate ; end-view sub-oval. 

 From the London Clay of the Copenhagen Fields, near London. 



Var. 2. Plate V, fig. 19. 



? Cytiierella intermedia, Bornemann. Zeitsch. Deutsch. geol. Ges., vii, p. 355, t. 20, fig. 3. 



inch. 

 Length, -Jg Lower Eocene : London. 



In this variety the valves are narrower and less square than in Var. 1 (fig. 18), and the 

 punctation is obscure and partial ; the convexity of the valves is more uniform, the 

 anterior portion not being so much depressed as either in Var. 1, or in the typical form. 



From the London Clay of Copenhagen Fields. 



No. 2. Cytherella Londinensis, spec. nov. Plate V, figs. 20, 22. 



INCH. 



Length, ^\ Lower Eocene : London. 



Carapace nearly oblong, rounded at the ends, dorsal border slightly curved, sloping 

 more rapidly towards the posterior than towards the anterior margin ; ventral margin 

 slightly incurved at the middle; left valve much narrower than the right; valves 

 smooth, depressed, marked by an irregular triangular impression, sub-central and 

 towards the dorsal edge [not well shown in the figures], and bearing slightly raised 

 narrow marginal rims, variable in development ; convexity nearly uniform, slightly 

 stronger on the anterior than on the posterior moiety of the valves. 



Dorsal profile narrow sub-oblong, slightly produced at the ends ; end-view sub- 

 oval. 



Cytherella Londinensis is from the London Clay of the Copenhagen Fields, near 



