THE CRETACEOUS FORMATION. 
3 
use of the term Cytherina, introduced by Lamarck Munster, however, in his paper 
‘On Some Fossil Species of Cypris and Cythere,’^ had retained Muller’s original 
generic appellation, Cytheref to which we return after the example of Latreille,^ 
Baird,® Milne Edwards,® &c. 
Dr. Reuss'^ has classified his species into “ SimpUces” Maryinatce” “ Cornuta,” 
and “ Concentricce.” The “ Simplices” comprise Cytherella, nob., which may justly be 
termed “ Simplex,” and Bairdia, M‘Coy, which differs materially from the last ; 
“Marginatse” and “Cornutse” divide Cythereis, nob., between them; and the “ Concen- 
tricse” are analogous to Cythere ynoper^ which, however, has by no means always 
concentric markings. 
M. Bosquet’s Cytherincs comprise the sub-genera Cytherella, nob., and Bairdia, 
M‘Coy, and to Cythereis and Cythere proper he has applied the generic appellation 
Cypridina, used by MM. Milne Edwards and de Koninck to designate a very different 
form of branchiopod, in wdiich genus M. Bosquet’s Cyprella ovidata^ and Cyprella 
KonincJciancd ought most probably to be placed. 
Previous to making any observations on the species which we have collected from 
the English Chalk and its accompanying strata, it will be necessary to take a rapid 
view of the characters of some of the recent Branchiopoda. 
The Entomostraca, Muller, composing Latreille’s Second General Division of 
Crustacea,^® and previously to Muller’s investigations known as the Monoculi,” are 
minute, insect-like animals, found in fresh, brackish, and salt water. Their bodies are 
furnished with a horny tegument of slender consistence, variously shaped in different 
families. This carapace in some resembles a cuirass, in others a shield, and in a 
large section it is very similar to the bivalve shell of a mollusc. Hence the appellation 
“shell insects,” given them by O. F. Muller in his elaborate monograph on these 
minute Crustaceans. 
The entomostracous Crustaceans which possess masticatory organs and have 
branchise attached to the feet and jaws are comprised in the Legion Branchiopoda. 
^ Hist. Nat. Anim. sans Vertebres, 1st edit. 1818. ^ Jahrbuch fiir Miner. &c. 1830. 
® Entomostraca, &c., p. 36, 1785. Hist. Nat. Crustaces, &c., tome iv, p. 249, 1801. 
® Mag. Zool. Bot. vol. ii, p. 138, 1838. ® Hist. Nat. Crustaces, &c., tome iii, 1838. 
^ Op. cit. p. 104. ® Op. cit. p. 22, pi. iv, fig. 4. ® Op. cit. p. 22, pi. iv, fig. 5. 
For Latreille’s classification and general history of the Crustacea consult the fourth volume of 
Cuvier’s ‘ Regne Animal,’ sec. edit. 1829 ; the thirteenth volume of Griffiths’s ‘ Translation,’ 1833 ; the third 
volume of Henderson’s edition, 1837 ; and Westwood’s ‘Translation,’ 1848. See also ‘Penny Cyclopaedia,’ 
vol. V, art. Branchiopoda and vol. ix, art. Entomostraca. For the bibliography and anatomy of the 
Branchiopoda consult Dr. Baird’s elaborate papers on the British Entomostraca, in the first and second 
volumes of the ‘Magazine of Zoology and Botany,’ 1837-8; in the ‘Annals Nat. Hist.,’ vol. i, 1838; 
‘Annals and Mag. Nat. Hist.,’ vol. xi, 1843 ; vol. xvii, 1846 ; and second series, vol. i, 1847 ; and in the 
‘Transactions of the Berwickshire Naturalists’ Club,’ vol. i. No. 3, 1835 ; and vol. ii. No. 13, 1845. See 
also M. Milne Edwards’s ‘ Hist. nat. des Crustaces,’ tom. iii, pp. 391 et seq. 
