12 
THE ENTOMOSTRACA OE 
they occur in this argillaceous deposit, we have the opportunity of studying them in 
all stages of growth. 
We conceive that M. Bosquet’s C. Bcemeriana cannot be said to differ in any 
essential point from M. Cornuel’s C. sculpta, which latter, if our observations on the 
stages of growth be correct, is only the unworn adult form of C. punctatiila, Roemer ; 
whilst the figure and description of C. punctatula are sufficiently characteristic of the 
species which Dr. Reuss and Mr. Williams have named t7. concentrica, to enable us to 
place the whole under the above-mentioned specific appellation used by M. Roemer, 
who found this species in the Hils-clay of Hilse. 
Variety, Virginea. fig. 2 n. 
Detritus, Charing. Chalk, Gravesend. 
This variety is similar to the above in every respect, except that it is devoid of 
supeidicial reticulations, wrinkles, or punctations ; some valves, however, viewed by 
transmitted light, show faint traces of a reticulated structure. 
Forms of Cythere allied to the above occur in the Oolites, supplying the majority 
of species to the Forest-marble, Fuller’s Earth, Upper Oolite, &c. They are also 
plentiful in the Tertiary beds and in the recent state. 
No. 3. Cytheke umbonata, Williamson. Tab. II, fig. 3 a — g. 
Cytherina umbonata, Williamson. 1847. Trans. Manchest. Phil. Soc. vol. vhi. Memoir 
on some, &c., p. 82, pi. iv, fig. 78. 
INCH. 
Length Jq Chalk-marl, Dover. 
Height Detritus, Charing. 
r inclusive of lateral projections, Chalk, Norwich and Woolwich. 
Thickness f 
[ exclusive of lateral projections, 
Carapace irregular oblong. Valves sub-concentrically punctated, in the young- 
individual depressed, convex in the adult, at all ages bearing a strong, oblique process, 
spine, or umbo, hollow and conical, placed on the median line, and rather posteriorly. 
Dorsal edge straight ; ventral somewhat elliptical. Anterior extremity rounded, slightly 
bearded ; posterior oblique, subacute at its dorsal angle. The hinges are but feebly 
developed ; the distance between the anterior and posterior hinge is greater than in 
the generality of the species of this group. 
Dorsal and ventral aspects four-lobed, somewhat cruciform ; posterior irregularly 
pentagonal. 
This rare and interestiag species, first noticed by Mr. Williamson, in the ‘ Trans- 
actions of the Manchester Philosophical Society,’ as occurring in the Charing Detritus, 
is found also in the Dover Chalk-marl, and in the Chalk of a few localities. 
