2 THE ENTOMOSTRACA OF 



the English with the foreign Cretaceous Entomostraca. With regard to the generic 

 arrangements adopted in the palseontographical works x'eferred to, I shall only observ'e 

 that, for the most part, the fossil carapace-valves have been studied and arranged with 

 but an indifferent knowledge of the relations of the carapace and animal. Hence, as 

 soon as the misapplication of the generic term " Cypridina " to the CytherincB was 

 corrected, the sub-generic divisions of Bairdia, Cytherella, &c., were erected into 

 independent genera on account of difference of carapace-structure ; a reason which does 

 not appear to me to be substantial, but requires other accompanying differences of 

 organization in the animal to render it good for generic distinctions. As far as we yet 

 know, the animal of Bairdia resembles that of Cythere proper, and so does that of 

 Cytheridea, judging from Dana's figui'e of Cythere Americana^ and Zenker's figure of 

 C. viridis? The animals with the other forms of carapace (CytUereis, Cytherella, &c.), 

 although they exist, have not yet been met with alive. 



If future investigations in the Cytherince by such close observers as Zenker and 

 Liljeborg should determine the existence of differences in internal organization (as 

 these authors already have in the Cyprinoi) among animals which differ but slightly in 

 the character and arrangement of the masticatory and locomotive limbs, the division of 

 Cythere into genera will become necessary; but at present, with carapaces only before 

 us, however these may differ among themselves, I think we had better keep the genus 

 intact, and regard the subordinate forms of carapace (which often pass insensibly from 

 one to another) as indicating only sub-genera or artificial divisions, convenient in the 

 studies of zoologists and palaeontologists. 



By pointing out, in my former Monograph, how frequently one and the same form 

 of carapace among the Ostracoda was repi'esented in different eras — in strata greatly 

 differing in age, or in recent seas as well as even sometimes in palaeozoic deposits — 

 I have so much astonished some Continental palaeontologists (who have found it 

 necessary to point out that I have mixed together what they regard as " incongruities," 

 both geological and palaeontological),^ that I shall abstain from troubling myself with 

 enumerating ail the close resemblances of form, and limit myself to the most obvious, 

 assuring my readers that these incongruities do exist, and that very similar forms of 

 carapace, both in the Ostracoda and in other Entomodraca, occur throughout nearly all 

 epochs; although each geologic division of time has nevertheless had its peculiar /ac/es 

 as regards the Entomostraca, as it has had of other groups of animal existences. 



i Dana's 'Crustacea,' pi. 89, fig. 9. ^ 'Archiv f. Nat.,' 1854, t. 4, fig. 10, &c. 



■^ Pictet 'Traite de Paleontologie,' 2d edit., vol. ii, p. 532 ; Reuss, 'Zeitsch. Deutsch. Gaol. Ges.,' 

 vol. vii, p. 278. 



