38 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



above the Spirorbis Limestone. These occur in North Staffordshire, in the 

 Blackband Ironstones. In a downward direction these shells are rarely found 

 below the Millstone-grit, or even in these beds except in Scotland, and perhaps 

 the north of England ; and this is probably due to the fact that in England the 

 Yoredale and Lower Limestone series (stages A, B, and C of Professor Hull) are 

 essentially and probably wholly marine ; while in Scotland and the north of 

 England marine appear to have alternated with fresh-water conditions. 



ASIPHONIDiE (Integropalliata). 



Glass PELECYPODA (Lamellibranchiata). 



Family UNIONIL\E. 



Genus Carbonioola, M'Coy, 1855. 



Synonyms : 



TJnio, Retzius, 1788. 



Mya, Martin, 1809. 



Unio, Sowerby, 1829. 



Pachyodon, Brown (non Stuchbury), 1843. 



Cardinia (in part), Agassiz, 1841. 



— -De Koninck, 1842. 



Anthracosia, King, 1856. 



— Amalizky, 1893. 



Naiadites (in part), Dawson, 1860. 

 Carbonicola, Amalizky, 1893. 



Generic Characters. — Equivalve, inequilateral, ovate or elongated, umbones 

 convex, raised above hinge-line, sometimes eroded, generally anterior, beaks more 

 or less contiguous, and with well-marked oval lunette in front of them. Anterior 

 part of shell broad and tumid, posterior narrower and slightly compressed. A 

 shallow, oblique, broad constriction, most marked at lower border, is situated a 

 little posterior to the middle of the shell in most species. Anterior border 

 bluntly curved, posterior narrow, truncated, curved, or angulated. 



