THE SHELL-LIMESTONE OF DURHAM. 139 



CYTHERE, MulUr, 



Sub-genus BAIRBIA {M'Coy). Jones' "Monograph of the 

 Entomostraca of the Cretaceous Formation of 

 England," p. 22 ; and " Monograph of the Ter- 

 tian Entomostraca of England, p. 51. 

 Balrdia (genus), M'Coy, 1844. " Syn. Char. Carb. 

 Foss. of Ireland," p. 164. 



This group was instituted by Professor M'Coy, in 1844, for 

 the reception of two species of Entomostraca, from the carboni- 

 ferous rocks of Ireland, which he considered to differ generically 

 from any existing genus. 



Mr. T. Rupert Jones, in his " Monograph of the Entomostraca 

 of the Cretaceous Formation of England," 1848, proposed its 

 adoption as a sub-genus of Cytliere, giving a good definition of 

 its sub-generic characters, which had scarcely been done by 

 M'Coy. I attach to it a similar value in these remarks. 



Mr. Jones has given further illustrations of the sub-genus in 

 his " Monograph of the Tertiary Entomostraca" (Palseonto- 

 graphical Society, 1856). 



Dr. Baird has placed it, as modified by Jones, among his syno- 

 nyms of Cythere. He states that no anatomical difference exists 

 in the animal of those recent species referred to it by Jones, from 

 the animal of Cythere proper.* This is certainly a strong point 

 in support of its near affinity with Cythere ; but still, with its 

 marked peculiarity of carapace, I think it may be fairly entitled 

 to a distinctive term, to mark it from the typical forms of 

 Cythere. At least, whether it really be a natural sub-genus or 

 not — supposing such to exist — it is a very convenient group in 

 paleontology, as it serves to mark a number of fossil Entomos- 

 traca of peculiar character, which have repeatedly held no unim- 

 portant position in the economy of ancient faunas. 



The sub-generic characters of Bairdia have already been given 

 by Mr. Jones. The Permian species add little that is new to 

 them, though it may be well to recapitulate the sub-generic fea- 

 tures of these forms. They all appear to be smooth ; sometimes 



* " Natural History of the British Entomostraca" (Ray Society), p. 163. 



