THE TERTIARY FORMATION. 7 



Sub-fam. 2. CytheriNjE {Cytheridce, Baird). Pedes numero sex, toti tenues, con- 

 similes, pediformes. 



Genus 1. Cythere, Miiller. Testa tenuis, lavis. Cauda brevis. 



Genus 2. Cythereis, 1 Jones. [Sub-genus, Jones.] Testa ruyulis vel tuberculin 

 ornata. {Animal iynotum. An hujus sedis ?) 



Fam. II. Halocyprid^e. 



Sub-fam. 1. Cypridinin^e. 



Genus 1. Cypridina. 2 

 Sub-fam. 2. Halocyprin^e. 



Genus 1. Conch^ecia. 



Genus 2. Halocypris. 



The minute anatomy of the internal organs supplies some very important charac- 

 teristics in addition to those derived from the limbs. Zenker, who has published" 

 copious anatomical details of the internal organization of some of the Cyprina and 

 Cyt/terina, and has somewhat modified the generic arrangement of the former group, 

 has still other species to examine before a complete classification on his plan can be 

 arrived at. This observer finds reason to divide the Cypris of authors into Cypris 

 proper, a sub-genus Cypria, and a genus Cyprois. 



The elaborate and highly illustrated work by M. Liljeborg, of Lund, published in 

 1853, has added greatly to our knowledge of the anatomical structure of a considerable 

 number of species of Cypris, as well as of other genera of Entomostraca ; and, by his 

 careful comparison of the Swedish species with published descriptions (as far as the 

 figures and descriptions of former authors serve), this author has advanced the 

 arrangement of specific forms. 



1 Cythereis was not established by me as a genus, but as a sub-genus. See ' Monog. Entom. Cretac.,' 

 p. 14. Its animal was unknown in 1849, and still remains so ; and the gradual passage of the carapace of 

 Cythereis into that of Cythere proper was too well recognised to allow of the difference of the two forms 

 being dwelt upon in any other light than as sub-generic, and as a convenient distinction for the sake of 

 palaeontologists. My friend Dr. Baird, from whose beautiful work on the ' British Entomostraca ' (Ray 

 Society, 1850) Dana has apparently derived his information on this point, recognising the marked difference 

 between some extreme forms of recent Cythereis and that of the common Cythere, figured and described 

 some carapaces of the former as generically distinct, and inadvertently omitted, when enumerating the 

 synonyms (p. 174), the word "sub-genus " in his reference to my detailed description of the carapace of 

 Cythereis. On subsequently seeing a series of the various modifications of the carapace in fossil specimens 

 of Cythere and Cythereis, Dr. Baird has expressed himself quite willing to regard the latter as a sub-genus, 

 until something at least is known of the animal itself. 



2 M. Liljeborg has also established a cognate genus, Philomedcs. (' De Crustaceis,' &c, 1853, p. 175.) 



3 'Archiv f. Anat.,' 1850; 'Archiv fur Naturgeschichte,' for 1854. 



