THE CRETACEOUS FORMATION. 
21 
No. 8. Cythereis cornuta, Bcemer. Tab. V, fig. 13 a — e. 
Cytherina cornuta, Ucemer. 1838. Jahrbucli f. Min. p. 518, n. 31, pi. vi, fig. 31. 
— — Beuss. 1845. Verst. Bolini. Kreid. p. 105, n. 15, pi. xxiv, fig. 20. 
Cypridina serrulata. Bosquet. 1847. Ent. foss. Maestricht, pp. 20, 414, pi. iv, fig. 2 a — d. 
YOUNG. ADULT. 
Length, 
INCH. 
1 
'3'3‘ 
INCH. 
1 
■3-0 
Gault, Folkstone. 
Height, 
1 
•^0 
1 
^3- 
Detritus, Charing. 
Thickness, 
1 
8^^ 
Chalk, South-East England. 
Tertiary Eocene, Paris {Bcemer). 
Chalk-marl, Bohemia (Beuss). 
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 rounded, 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. Roemer as occurring in the Tertiary beds near Paris, 
and by Dr. Reuss as being found in the Bohemian Chalk Formation. C. serrulata. 
Bosquet, of the Maestricht Chalk, does not appear to differ materially from C. cornuta, 
Roemer. 
No. 9. Cythereis alata. Bosquet. Tab. V, fig. 14 a — d. 
Cypridina alata. Bosquet. 1847- Entom. foss. Maestricht, p. 19, n. 13, pi. iv, fig. 1 a — d. 
INCH. 
Length, Detritus, Charing. 
Height, Chalk, Norwich, Gravesend, and Charlton. 
Thickness, 
Chalk, Maestricht (Bosquet). 
CarajMce 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 
