CLASSIFICATION OF THE OSTRACODA. 109 



§ VII. CLASSIFICATION OF THE OSTRACODA. 



The remains of Entomostraca occurring in the Post-tertiary formations belong, so far 

 as we at present know them, exclusively to the Ostracoda, nor is it likely that an 

 extension of our knowledge will reveal the presence of any other tribes in the British 

 area. The soft or chitinous nature of the investments of the other groups renders their 

 speedy putrefaction almost inevitable, except, perhaps, with some of the Phyllopoda, 

 which are for the most part confined to warmer waters than any which have existed in 

 this region in recent times. ^ 



The only satisfactory classification of these creatures being based upon the structure 

 of those parts which most rapidly disappear after the death of the animal, it would be 

 of little use in this place to give tables which must refer only to details altogether beyond 

 the scrutiny of the palaeontologist. We may, however, refer the reader for information 

 on this subject to the memoir of Dr. G. 0. Sars on the ' Marine Ostracoda of Norway,' 

 and to Mr. G. S. Brady's ' Monograph of the Recent British Ostracoda,' published by 

 the Linnean Society. But as being of more utility to the student of fossil species we 

 have drawn up a table embracing only the characters derived from the shells without 

 any regard to internal animal structure ; this is the more feasible inasmuch as the 

 affinities of internal anatomy are always found (as might, by a believer in the doctrine of 

 evolution, be fully expected) to correspond more or less closely with similar affinities of 

 shell-structnre. To make our survey of the Ostracoda more complete, and for the sake 

 of assigning to their proper position several genera, which have hitherto been published 

 only in a disconnected manner, we, however, here insert a synopsis of the anatomical 

 characters of the species belonging to the families Cypridge, Darwinellidse, and 

 Cytheridae ; and we give likewise a list, revised up to this date, of the families and 

 genera of the Ostracoda, recent and fossil, so far as they are known to us. 



• The only instance within our knowledge in which remains of Cladocera have been preserved in 

 the Post-tertiary formations is that of the Dipple Tile-works, referred to on a previous page. Fragments of 

 the chitinous limbs and investments of these creatures are here very abundant, and possibly, if they could 

 be examined in situ, might be found tolerably perfect, but the unavoidable processes of " washing," and 

 otherwise manipulating the matrix, reduce them to a very fragmentary condition before they can be 

 effectively submitted to microscopic examination. We have, however, been able to recognise with certainty 

 in the Dipple deposit, remains of Camptocercus macrourus (which constitute the bulk of the fragments), 

 and Alona elonguta, and, more doubtfully, Chydorus sphcsricus, Alona guttata, and Alona quadrangularis. 

 There are also in considerable abundance bodies which appear to be the ephippia of Daphniadce. 



