Vol. 57.] PENDLESIDE GEOXJP AT PENDLE HILL, ETC. 381 



three species, Nuculana attenuata, Nucula gibhosa, and Ctenodonta 

 Ic^virostris, but it seems that iV. attenuata always came in some little 

 time before the others. 



The three genera mentioned above all appear in the Calciferous 

 Sandstone Series of Scotland, and reappear in that area at many 

 horizons in the Carboniferous Series up to the top of that sub- 

 division. 



According to Mr. J. W. Kirkby's tables^ Nuculana {Leda) 

 attenuata is found 3000 to 3800 feet below the Carboniferous 

 Limestone, at a lower horizon than Nucula gibhosa, which comes 

 in from 500 to 2300 feet below that bed. Ctenodonta Icevirostris 

 is not mentioned by him, and we have been unable to give the 

 £xact point at which it first comes in, but in the upper part of 

 the Calciferous Sandstone Series of Eife all these fossils are found 

 together. They never occur in the pure white or grey limestones, 

 only in the shales between them. 



In the West of Scotland these species are well represented in the 

 shales of the Carboniferous Limestone Series. Mr. J. Smith, of 

 Kilwinning, informs us that they have not been found below the 

 * shale' under the lowest 'post' of the Lower Limestone Series. 



The Calciferous Sandstone Series in Eskdale, however, does not 

 seem to possess these species, though they all come in in the shales 

 associated with the limestones on the horizon of the Hurlet Lime- 

 stone. Parther south, in jS'orthumberland, Nucidana attenuata, 

 Nucula gibbosa, and Ctenodonta Icevirostris are absent in the Tuedian 

 •Series ; iV^. attenuata comes on alone in the Carbonaceous division, 

 but N. gibbosa is found with it in the shales of the Calcareous 

 division above, at several horizons. 



Still farther south, the lowest horizon at which we have been 

 able to obtain Nucidana attenuata and Ctenodonta Icevirostris in the 

 valley of the Eden, is in shales presumably above the Underset 

 Limestone. They probably do occur somewhat lower, however, 

 -for we have obtained Ctenodonta Icevirostris in shales below the 

 Hardraw Scar Limestone, although at present Nuculana attenuata 

 and Nucula gibbosa are not known so low down in this locality. 

 'Farther south again, in beds presumably immediately above the 

 main mass of limestone at Whitewell, Nuculana attenuata and 

 Ctenodonta Icevirostris appear, the latter being found at more than 

 one horizon in the Pendleside Group. 



Continuing in a southerly direction, we find in the Marsden 

 Valley, at Eccup near Leeds, and Congleton Edge (Cheshire), the 

 lowest horizon for Nucula gibbosa and Ctenodonta Icevirostris in the 

 upper part of the Pendleside Group and Shales below the Third 

 Grit ; while these shells are found at one or more horizons in the 

 -Coal-Measures of Lancashire and North Staffordshire. Nucidana 

 xittenuata has disappeared, but its place has been taken by Nuculana 

 stilla. 



This peculiar distribution of allied forms of shells is very 

 rstriking, and seems to us to point conclusively to the fact that the 



"^ Quart. Journ. Geol. Soc. vol. xxxvi (1880) p. 589. 



2d 2 



