CRUSTACEA. 



157 



Cythere, and Bairdia are represented by species now living. 

 Presumably all these genera were marine, and we know that 

 this was the case with many of them. The Devonian rocks 

 are comparatively poor in Ostracoda, all the known forms 

 (leaving Estherid out of consideration) belonging to the genera 

 Entomis, Leperditia, and Beyrichia. In the Carboniferous 



Fig. 100. Fossil Ostracode Crustaceans : a Primitia strangitlata, Lower Silurian ; 

 b Primitia Logani, Lower Silurian ; c Beyrichia Klaedeni, Upper Silurian ; d d' 

 CytJierella inflata, Carboniferous; e Leperditia Anna, Lower Silurian ; f Leperditia 

 Canadeusis, Lower Silurian ; g Beyrichia impendens, Upper Silurian ; h Beyrichia 

 subarcuata, Carboniferous ; i Candona Tateana, Carboniferous. All enlarged. 



Rocks no less than fifteen genera have been detected. Of 

 these the genera Leperditia, Bairdia, Beyrichia, Cythere, Cypri- 

 dina, Cypridella, and Entomis are the most important. The 

 Leperditia were formerly referred to the genus Cypris, the 

 species of which are exclusively fresh-water in their habits. It 

 is noticeable, however, that some of the Carboniferous species 

 have been referred, apparently on good grounds, to the recent 

 genus Candona, all the forms of which inhabit fresh water. It 

 is also noticeable that the genera Beyrichia and Entomis 

 appear to die out in the Carboniferous Rocks, and have not 

 been detected in any later formations. In the Permian Rocks 

 we have only the genera Bairdia, Cythere, and Cypridina, of 

 which the two former are represented by living forms. In the 

 Secondary and Tertiary deposits, remains of Ostracode Crust- 

 aceans are abundant, often occurring in myriads in certain 

 strata, to which they sometimes impart a fissile character. The 

 chief genera which are represented in Mesozoic and Kainozoic 

 time, are Cypris, Candona, Bairdia, Cythere, Cytherella, and 

 Cypridina, all of which are represented by living species at the 

 present day."' 



r The facts here summarised are mainly drawn from the Memoirs of 

 Professor Rupert Jones, and his admirable Monographs on the Ostracoda, 

 published by the Paloeontographical Society. 



