584 MR. H. BOLTON, P.R.S.E., ON [June, 1904. 



rest of the Middle Measures, and closely akin to that of the 

 Lower series, whilst it is also purely local, we may regard 

 the Brachiopoda for all practical purposes as non-existent in 

 the fauna of the ordinary strata of the Middle series. 



Biscina orbicularis (Bolton). 



"Marine Band," Ashton Moss Colliery, Audenshaw. 

 (L. 2620, e. coll. Cairns, M.M.) 



Lingula sp. 



Ashton Moss Colliery, Audenshaw. (e. coll. Cairns, 

 M.M.) 'No horizon is given with this fossil. Probahly L. 

 3545, 3546 and 3547, e. coll. Cairns, also belong to the same 

 horizon and place but no history is attached to them. 



Pelecypoda. 

 The general character of the molluscan fauna is similar to 

 that of the Lower Measures. The number of genera and 

 species has increased. Eliminating all doubtful forms, we 

 find that eight genera, and twenty species of bivalves are 

 present in the Lower Coal Measures, whilst the Middle 

 possess thirteen genera and thirty-eight species. Four 

 genera and twelve species come up from the Lower into the 

 Middle Measures. The main increase of species is in the 

 three genera Naiadites (Anthracoptera), Carbonicola 

 (Anthracosia), and Anthracomya, the members of which 

 are especially characteristic of the Middle Coal Measures, 

 occur over a wide area, and have a considerable 

 range. The Carbonicola (Anthracosia) are of extreme 

 interest owing to the association of several species at the 

 same horizon, and the great extent of varietal development. 

 (Several species can be linked up by means of varietal forms, 

 and there seems no doubt that a considerable amount of 

 interbreeding existed between the forms now regarded as 

 valid species. In the accompanying list, certain forms are 



