2l8 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



aria, or those occurring in the Millstone Grit and Lower, Middle, 

 and Upper Coal-measures. With the exception of the Lower Coal- 

 measures, which have yielded 12 genera and 42 species, the three 

 remaining horizons are comparatively poor, as would be anticipated 

 from the estuarine condition or nature of the deposits. Anthracosia, 

 Anthracoptera, Aoeinus, Ctenodonta, Edmondia, Modiola, Myacites, 

 Myalina, and Schizodus are the genera that characterize the Coal- 

 measures, or beds above the Yoredale series. 



6 genera and 9 species are all that are known from the Millstone 

 Grit ; the genera are Anthracosia 2 species, Axinus 1, Ctenodonta 3, 

 Edmondia 1, Lunulacardium 1, Myacites 1. 



The genera in the Lower Coal-measures, 14 with 44 species, are 

 still more estuarine in habit, many allied to the Unionidae and 

 Myadse — Anthracomya 5 species, Anthracosia 6, Anthracoptera 2, 

 Aocinus 2, Oonocardium 1, Ctenodonta 6, Edmondia 3, Leptodomus 1, 

 Modiola 4, Myacites 4, Myalina 6, Pleurophorus 1, Pullastra 1, 

 Schizodus 2. The Middle Coal-measures have, as yet, only yielded 

 4 genera and 16 species— Anthracomya 6 species, Anthracosia 6, 

 Anthracoptera 2, and Myalina 2 species. The Upper Coal-measures 

 contain the same 4 genera with 11 species. The above, with the 

 table of distribution, clearly shows the changes from the deeper-sea 

 fauna of the Limestone series to the shallow and estuarine accumu- 

 lations of the Coal-measures, the gradual dying-out of those genera, 

 essentially dwellers in clear and deep water and with associated 

 sedimentary matter, as well as the almost total extinction of the 

 molluscan fauna with the elevation of the sea-bed, a few genera 

 only living on into the Permian sea. 



The accompanying Table gives the numerical value of the species 

 of 18 of the chief Dimyarian genera out of 43 for England, Scot- 

 land, and Ireland ; also Belgium, for comparison, which is the only 

 country in Europe where the Carboniferous rocks (Lower series) are 

 well developed. The researches of Prof. De Koninck, of Liege, have 

 afforded mo data for this column. I have before stated the small 

 number of known species in the European area beyond Belgium ; to 

 show, however, the relationship between the American fauna and 

 our own, I have appended a column also, which shows excess in the 

 number of species in most of the genera. Such holds good with the 

 older Palaeozoic genera also ; but, through the flora and Mollusca of 

 the Coal-measures, America and Scotland are intimately associated, 

 and, in a similar but less degree, Ireland, 



