THE CRETACEOUS FORMATION. 3 



use of the term Cytherina, introduced by Lamarck •} Miinster, however, in his paper 

 'On Some Fossil Species of Cypris and Cythere,'^ had retained Miiller's original 

 generic appellation, Cythere^ to which we return after the example of Latreille/ 

 Baird/ Milne Edwards/ &c. 



Dr. Reuss^ has classified his species into " Simplices," " Maryinatce" " Cornuta'' 

 and " ConcentriccB." The " Simplices" comprise Cytlierella, nob., which may justly be 

 termed "Simplex," and Bairdia, M'Coy, which differs materially from the last; 

 "Marginatge" and "Cornutse" divide Cythereis, nob., between them; and the "Concen- 

 tricse" are analogous to Cythere j^t'oper, which, however, has by no means always 

 concentric markings. 



M. Bosquet's Cytherina comprise the sub-genera Ctjtlierella, nob., and Bairdia, 

 M'Coy, and to Cythereis and Cythere 2)roper he has applied the generic appellation 

 Cypridina, used by MM. Milne Edwards and de Koninck to designate a very different 

 form of branchiopod, in which genus M. Bosquet's Cyprella ovulata^ and Cyprella 

 Koninchiana^ 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 wdth 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. 



1 Hist. Nat. Anim. sans Vertfebres, 1st edit. 1818. = Jahrbucli fur Miner. &c. 1830. 



3 Entomostraca, &c., p. 36, 1785. * Hist. Nat. Crustaces, &c., tome iv, p. 249, 1801. 



5 Mag. Zool. Bot. vol. ii, p. 138, 1838. ^ Hist. Nat. Crustaces, &c., tome iii, 1838. 



'' Op. cit. p. 104. 8 Op. cit. p. 22, pi. iv, fig. 4. ^ Qp. cit. p. 22, pi. iv, fig. 5. 



10 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,' torn, iii, pp. 391 et seq. 



