"Vol. 57.] PBNDLESIDE GROUP AT PENDLE HILL, ETC. 383 



examination of the specimen \re are not able to recognize that it 

 belongs to that genus. 



Farther south, in the Yorkshire dales, the three genera have not 

 been found either in the Great Scar or in the Yoredale Series. In 

 the Pendleside Group, Messrs. J. Barnes & W. P. Holroyd have found 

 three species of Carbonicola and one of Naiadites in rocks, pre- 

 sumably of , this horizon, at Pule Hill Tunnel, near Marsden. 



Still farther south, in Staffordshire and Derbyshire, these genera 

 only come in at the base of the Coal-]\Jeasures, but they are each 

 represented by numerous species. 



If the horizons, at which a large number of the marine fossils 

 of the Calciferous Sandstone Series of Fife occur in other districts, 

 were noted, similar isodietic lines would be shown. In the case 

 of the lamellibranchs, which we have chosen for the investigation 

 (1) because they are now fairly well known ; (2) because we were 

 able to distiiiguish the species with some approach to accuracy ; and 

 (3) because in the adult stage they do not possess active means of 

 migration, the isodietic line for the whole lamellibranch fauna 

 of the Calciferous Sandstone Series lies within very narrow limits. 

 It is practically identical with that of the Nuculidge : that is to say, 

 as one passes southward, a large part of the fauna of the Calciferous 

 Sandstone Series occurs at continuously higher horizons, showing the 

 gradual southward spread of similar conditions of environment. 

 Many of the lamellibranchs of the Calciferous Sandstone Series 

 preferring muddy and tuibid waters, evidently could not live in 

 the clear waters where limestones were accumulating. Thus it may 

 be inferred that as Carboniferous times went on, the influence of 

 the land was felt farther and ever farther south, as is shown by 

 the tendency to interruption of the deposition of limestone by detrital 

 shales and sandstones, and eventually the complete cessation of 

 the formation of pure limestones, even in the area of maximum 

 deposition. 



With regard to Aviculopecten papyraceus, which we have chosen 

 as a zonal form, it is interesting to note that it occurs at a lower 

 horizon in Scotland than it does in England. 



It is found in shale at East Kilbride, 2| feet above the Calder- 

 -wood Cement-Stone at Glebe Quarry, which is supposed to belong 

 to the Lower Limestone Series of Scotland ; but it seems possible 

 that the beds really belong to the Upper Limestone Series, for litho- 

 logieal and palaeontological reasons. In Northumberland this 

 species does not seem to go below the base of the Coal-Measures, 

 but it occurs in the Pendleside Group and passes up to the Coal- 

 Measures in the iS'orthern Midlands. 



Chondes Layuessiana appears to be an important species, on 

 account of its almost universal occurrence in the Pendleside Lime- 

 stone localities. It occurs in large quantities in Scotland, round 

 Beith, in the Shales of the Lower Limestone Series, In the York- 

 shire dales it occurs in the shales between the various Yoredale 



