10 
THE ENTOMOSTRACA OF 
numerous, and we have not found more than four or five additional forms in the Lias 
and in the Lower and Upper Oolites. In the Tertiary Formation, however, and in the 
recent state the species are far more varied and abundant. 
No 1. Cythere Hilseana, Roemer. Tab. I, fig. 1. a — -y. 
Cytheeina Hilseana, Rcetner. 1840. Verstein. Nordcleutsch. Kreid. p. 104, n. 1, pi. xvi, fig. 17. 
— — Reuss. 1845. Verstein. Bohm. Kreid. p. 16, pi. v, fig. 39 a, b. 
Length, 
Height, 
Thickness 
INCH. 
i„ 
3 0 
1 
’ To 
1 1 
23 - 
4 ^ 
3-0 
Greensand, Blackdown. Eocene Sand, ColweU Bay, Isle of Wight. 
Gault, Folkstone and Leacon Hill. — Lower Fresh-water Formation, Isle of Wight. 
Chalk-marl, Dover. — Clay, Barton, Hants. 
Detritus, Charing. 
Miocene, Coralline Crag, Walton. 
Hils-clay, North Germany (Roemer). Chalk-marl and Chalk, Bohemia (Reuss). Chalk, Balsberg, Sweden. 
Carapace sub-triangular. Valves convex, finely punctate, and hairy.^ The internal 
surface of the valves is also covered with hairs, especially near the dorsal border. 
Dorsal border elliptical in the left (larger) valve, and rather angular in the right 
(smaller) valve ; ventral border almost straight. Anterior extremity obliquely semi- 
circular; posterior subacute, pointing obliquely downwards. Both extremities are 
provided with spines, especially on their inferior moieties. 
Dorsal aspect acute oval ; anterior ovate. 
Just within the anterior hinge each valve exhibits a small circular pit, peculiar to 
this species, marked externally by a corresponding protuberance. In C. Hilseana the 
hinges are less developed than in the generality of Cytheres, especially as regards the 
hinge-teeth, which are merely the knurled extremities of the hinge-bar ; and, contrary 
to what obtains in other species, the hinges are equally developed anteriorly and 
posteriorly. 
This species is abundant in the Gault, and is of frequent occurrence in the Chalk- 
marl and the Detritus, it is found also in the Greensand ; it is not present, however, in 
the English Chalk, although occurring in the Chalk of Bohemia and of Balsberg. It 
is described by M. Roemer as found in the Hils-clay® of Hilse, North Germany. 
An apparently identical species is found in the Lower Fresh-water (so-called) For- 
^ In this and the following instances each column of fractions represents the dimensions of an individual. 
2 The delicate external characters of this and other species are well preserved in the Gault. The 
specimens from the other Cretaceous strata have their markings and spines more or less worn. 
® The Hils-clay (Hils-thon), according to M. Roemer, is the lowest member of the Neocomian series, 
lying upon the Weald-clay, and representing the Speeton-clay, which latter, in M. Roemer’s opinion, belongs 
to the Neocomian group. (See Translation of Appendix to Rcemer’s North Germany Chalk Formation, in 
Taylor’s ‘Scientific Memoirs,’ vol. iv, art. 5.) 
