THE CRETACEOUS FORMATION. 21 



No. 8. Cythereis cornuta, Ewmer. Tab. V, fig. 13 a — e. 



Cytherina coenuta, Rcemer. 1838. Jahrbuch f. Min. p. 518, n. 31, pi. vi, fig. 31. 



— — Beuss. 1845. Verst. Bolim. Kreid. p. 105, n. 15, pi. xxiv, fig. 20. 



Cypridina sebedlata. Bosquet. 1847. Ent. foss. Maestricht, pp. 20, 414, pi. iv, fig. 2a — d. 



YOUNG. 

 INCH. 



Length, ^ 



ADULT. 

 INCH. 







Gault, Folkstone. 



Height, ^V 



oV 







Detritus, Charing. 



Thickness, Jj 









Chalk, South-East England 







Tertiary Eocene, Paris (Rcemer). 

 Chalk-marl, Bohemia (Reiiss). 

 Chalk, Maestricht (Bosquet). 



Carapace somewhat oblong. Valves depressed towards dorsal border, provided with 

 a strong, crenulated, marginal ridge, and bearing, when young, one or more irregular 

 tubercles besides the central tubercle, which is long and pointed. Anterior extremity 

 obliquely rovmded, shelving, strongly bearded ; posterior narrower, strongly depressed, 

 acute, partially bearded. 



Dorsal and ventral aspects of adult shell triangular ; of the young shell somewhat 

 sagittate, and its ventral surface longitudinally wrinkled. Anterior aspect irregularly 

 triangular. 



C. cornuta is not common. When young, it differs from the young form of 

 C. ciliata, Reuss, in being quite destitute of punctations, in the greater development 

 of its marginal ridge, in the different characters of its tubercles, in being wider 

 anteriorly, and in having a more depressed carapace. 



This species is described by M. Rcemer as occurring in the Tertiary beds near Paris, 

 and by Dr. Reuss as being found in the Bohemian Chalk Formation. C. serndata, 

 Bosquet, of the Maestricht Chalk, does not appear to differ materially from C. cornuta, 

 Rcemer. 



No. 9. Cythereis alata, Bosquet. Tab. V, fig. 14 a — d. 



Cypeidina alata. Bosquet. 1847. Entom. foss. Maestricht, p. 19, n. 13, pi. iv, fig. 1 a—d. 



INCH. 



Length, -^ Detritus, Charing. 



Height, jij Chalk, Norwich, Gravesend, and Charlton. 



Thickness, -^ 



Chalk, Maestricht (Bosquet). 



Carapace somewhat oblong. Valves smooth, shining, strongly convex on ventral 

 half, depressed towards the dorsal border ; a smooth, semicircular ridge lies near the 

 anterior extremity, and is extended along the raised ventral keel. Anterior extremity 

 rounded, shelving ; posterior narrow, suddenly depressed, each extremity having strong 



