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X. On New or imperfectly known Species of Marine Ostracoda. 

 By George Stewardson Brady. 



Read March 14, 1865. 



[Plates LVII.-LXIL] 



UF the sixty-seven species described in the following paper, ten have been identified 

 with forms already described and figured from fossil (chiefly Tertiary) specimens ; hvo 

 species, Bairdia suhdeltoidea, Miinster, and Cythere setosu, Baird, were already known 

 in the recent state, but appeared to require further illustration. The remaining 

 fifty-five species I have been unable to refer to any published forms', though many of 

 them have, as might be expected, very near relatives amongst the Tertiary fossils. The 

 ten fossil species of which descriptions are now given for the first time, from recent 

 specimens, are as follows : — Cytherella beyrichi, Reuss ; Bairdia ovata, Bosquet ; 

 Cytherideis gracilis, Reuss ; Cytheridea miilleri, Minister ; Cythere jurinei, Miinster ; 

 C. canaliculata, Reuss ; C. plicatula, Reuss ; C clathrata, Reuss ; C. subcoronata, Speyer ; 

 C. scabra, Miinster. 



The difiiculty of identifying Ostracoda merely by reference to figures and descrip- 

 tions is much increased by our uncertainty as to the characters which can rightly be 

 considered as indices of specific rank. A vast number of species have been founded on 

 peculiarities of surface-marking ; but it is quite certain that this, unless accompanied 

 by other distinctions, is in most cases a character upon which no reliance whatever 

 can be placed. The range of variation, in this respect, which may be observed in the 

 same species as the result of age or peculiarity of habitat, is very great, and may be 

 appreciated by reference to the figures (PL LIX. fig. 14, a-g) of Cythere mutabilis, 

 Brady, M.S. There is, indeed, scarcely any species which does not exhibit very great 

 variety of surface-marking : nevertheless, so far as my observation extends, the vari- 

 ation is always in the same direction for the same species ; that is to say, a species — 

 Bairdia subdeltoidea, for instance — may run through many shades of sculpturing, from 

 a perfectly smooth to a strongly punctate carapace, but the intermediate forms will be 

 characterized merely by greater or less development of the typical form of sculpture. 

 There will never be any tendency to a rugose, striated, tubercular, or any other system 

 of ornamentation. If such a deviation were observed, it would lead one to suspect a 

 specific difference^, 



' Since this was written, three of the species here described, Jonesia simplex, Cythere latissima, and Cythe- 

 ridea papulosa have been figured and described from British specimens by the Rev. A. M. Norman. 



' Yet, even in this respect, it is necessary to speak with some reservation ; for we find it an almost uniform 



