THE TERTIARY FORMATION. 33 



; Cythere plicata, Milnsfer. Jahrb. f. Min., &c., 1830, p. 63 ; and Neues Jahrb., &c. 



1835, p. 446. 

 Cytherina plicata, Eoemer. Neues Jahrb. f. Min., &c., 1838, p. 518, t. 6, fig. 26. 

 Cypridina plicata, Beiiss. Haidinger's Abhandl., iii, p. 4.3, t. 10, fig. 21. 



— laticostata, lb. Haidinger's Abhandl., iii, p. 87, t. 11, fig. 13. [C. plicata, var.] 

 Cythere plicata. Bosquet. Mem. Couron. Acad. Belg., xxiv, p. 60, t. 2, fig. 13. 



— (Cythereis) plicata, Jones. Quart. Journ. Geol. Soc, x, p. 162, t. 2, fig. 13. 



INCH. 



Length, -^^ Middle Eocene : Isle of Wight, and Hampshire. 



Upper and Middle Eocene : Europe. 



Carapace ovato-oblong ; anteriorly oblique, with the antero-ventral angle rounded ; 

 posteriorly narrower and obliquely rounded ; dorsal margin straight ; ventral margin 

 convex or somewhat sinuate : valves most convex at the posterior third ; bearing three 

 raised longitudinal ridges, — one on either side of, and parallel with, the median line of 

 the valve (the ventral one the most convex and gentl}^ curving downwards, the other 

 weaker and sinuous), and another (the third) ridge occupying the dorsal part of the 

 valve, shorter than the others and curved, its most convex central portion more or less 

 projecting over the dorsal edge ; the vehtral portion of the valve suddenly slopes 

 inwards and downwards from the summit of the ventral ridge, so as to form a blunt 

 keel to the closed carapace ; front and hind margins more or less denticulate : surface 

 of the valves usually ornamented with faint longitudinal wrinkles and obscure pittings 

 and reticulations on and between the ridges. 



Dorsal profile elongate-subovate, with angular ends; end-view broad-irregular-ovate, 

 modified by the lateral ridges. 



This species, like C. triplicata of the Chalk, is one of the passage-forms between 

 Cythere proper and Cythereis. 



Var. laticosfa (Reuss, Loc. cit.), from the Barton Clay of Hampshire, is decidedly 

 identical with the form (from the same deposit) figured at pi. 5, fig. 8 ; and is merely a 

 more ovate, shorter, plumper, and more strongly ribbed variety of C. plicata. 



This species has been found in the Miocene deposits of Dax, and in the Eocene of 

 France, Belgium, North-western Germany, Bohemia, Austria, and Moravia. It occurs 

 abundantly in the white Tertiary sands and in an Oyster-band at Colwell Bay, Isle of 

 Wight ; also in the clays at Barton, Highclifif, and Bracklesham, in Hampshire. 



The specimens from Colwell are opaque, white, and fragile ; those from the Hamp- 

 shire clays are brown, tough, and somewhat translucent. 



No. 17. Cythere scrobiculoplicata, spec. nov. Plate VI, figs. 4, 6e — 6 d. 



i>;cH. 

 Length, tjj . Lower Eocene : London. 



