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. 


ASIPHONIDA) (Inrecropatiiata). 
Class PELECYPODA (LaMELLIBRANCHIATA). 
Family UNIONIDA. 
Genus Carpontcota, M‘Coy, 1855. 
Synonyms : 
Unio, 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.—Kquivalve, 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. 
