PLATE XXIII. 



TJnless otherwise stated, the figures in each of these 

 plates are of the natural size, and reproductions of 

 original drawings by Mr. G. S. Barkentin. 



Fenestella subarctica (page 249). 



The type and only specimen of this .'-peoies known to the writer, from the 

 Silurian limestone of the Ekwan River, shewing the ceUuliferous side 

 of an imperfect zoarium, six times the natural size, and slightly 

 restored. 



