THE CRETACEOUS EORMATION. 
31 
No. 3. Cytherella Williamsoniana 
Var. 
YOUNG. 
ADULT. 
Granulosa. 
INCH. 
INCH. 
INCH. 
Length, 
6^ 
ao" 
1 
Height, 
1 
T(To 
1 
6 0 
1 
EG 
Thickness 
> 
1 
nohis. Tab. VII, fig. 26, a — i. 
Gault, Folkstone, and Leacon Hill. 
Chalk-marl, Dover. 
Detritus, Charing. 
Chalk, South-East England. 
Carapace depressed, oblong ; when young, approaching to oval. Valves flat, with 
a very shallow internal cavity ; having a smooth, convex ridge running close to the 
anterior margin, and dying out on the superior and inferior margins ; a similar but 
stronger ridge lies near the superior, inferior, and posterior borders of the valve, or 
rather, two strongly-developed longitudinal ridges, one near the superior, and the 
other near the inferior border, beginning on the anterior third of the valve, free of 
the marginal ridge, and within it, run baekwards to the posterior extremity of the 
valve, and are there more or less perfectly connected by a cross ridge. Between the 
anterior extremities of these ridges there are sometimes one or more short ridges or 
club-shaped tubercles. In old shells, at the superior and inferior angles of the posterior 
extremity of the valve, the ridge is developed into two large tubercles, having cor- 
responding cavities on the inner surface of the valve. Extremities rounded ; posterior 
extremity slightly bearded. Dorsal edge slightly arched ; ventral somewhat incurved. 
Dorsal and ventral aspects narrow, irregular, elongate-oblong; anterior irregular, oblong. 
Named after Mr. Williamson, of Manehester, who has devoted much time and labour 
to the investigation of the Entomostraca and other Mierozoa, both recent and fossil. 
Variety Granulosa, fig. 26 
Chalk, Norwich. 
In this shell, which arrives at a comparatively large size, the ridges and tubercles, 
especially the latter, are very strongly developed. The whole surface of the valve is 
covered with granulations, coarser in the depressions than on the ridges. It occurs 
rather plentifully in the Soft Chalk at Thorpe, near Norwich, and like others of the 
Entomostraca of that locality has a reddish-brown colour. 
This depressed form of carapace is not very common. Besides the above- 
mentioned speeies and its variety, there is one other speeies in the Maestricht Chalk, 
described and figured by M. Bosquet as Cypridina auricidaris (Op. cit. pi. iii, fig. 3), 
and another in the Carboniferous Limestone of East Kilbride,^ Scotland. 
’ In tbe Hunterian Museum, among the fossil microscopic shells from East Kilbride. See note, 2 ^. 2C. 
