83 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



along what lines the modern Unio has developed from a Mytiliform ancestor. 

 Mycetopus from the Parana and Amazon retains the edentulous hinge, expanded 

 posterior end, and subparallel margins which are so characteristic of Anthracomya ; 

 Anodon also has a very strong external resemblance, but I have never seen the 

 erosion of the umbones in any species of Anthracomya. The Anthracomya? are , 

 as a rule, comparatively rare, and form a very small percentage of the molluscan 

 remains at any horizon, although in one or two beds one species may occur 

 abundantly, in which case other shells are very seldom found. They had not, with 

 the exception of Anthracomya Phillipsii, the gregarious habit of Carbonicola and 

 Naiadites. The members of this genus are, as far as is known at present, 

 absent in the Upper Coal-measures, with one exception, A. Phillipsii; and are 

 chiefly found in the Middle Coal-measures of Lancashire, Yorkshire, and the 

 Midlands ; in Scotland, one species (A. Scotica.) occurs in the Calciferous sandstone 

 beds, and another (A. modiolaris) is found in beds of the Carboniferous limestone 

 group, and also in those of the true Coal-measures. The so-called Lower Coal- 

 measures of North Staffordshire really belong to the middle division, the Gannister 

 series being represented in this area by the lower beds only of the Biddulph 

 and Cheadle basins, where alone the fossils characteristic of the Yorkshire 

 and Lancashire gannister are to be found. In North Staffordshire an arbitrary 

 line is taken at the Ash or Rowhurst coal, which is said to be at the top of the 

 Lower Measures ; but there is neither lithological nor palceontological ground 

 for this division, which should be placed, I think, more correctly, if anywhere, 

 above the Bulhurst seam, where shales with Aviculopecten, Goniatites, Lingula, 

 and Posidonia occur in the Pottery coal-field, and at the Stinking coal shale of 

 the Cheadle coal-field, where a similar fauna is also to be found. Even in 

 Lancashire, beds full of Carbonicola are to be found in the Lower or Gannister 

 Coal-measures. 



In a letter last year, Mr. Kirkby drew my attention to the close resemblance 

 between Portlock's Modiola Macadami and its two varieties, and M. subparallela, 

 mid the sh ells of the genus Anthracomya. I figure two specimens, kindly lent me by 

 Mr. Wright, of Belfast, from the Coal-measures of Ballycastle, on PL XVII, figs. 1 

 mid 2, which seem to be characteristic of the form known as Modiola subparallela, 

 which Portlock states in his observations also merge into M. Macadami. The 

 original figure approaches very closely in contour to some forms of Anthracomya, 

 while M. Macadami, especially the variety elongata, would seem to resemble 

 Anthracomya Phillipsii. Portlock, however, goes on to say this variety approxi- 

 mates to M. lingualis, Phillips, a Mountain-limestone form. The Irish specimens 

 occur in hods of shale with large scales of Holoptychius r<ir!/<>c/ri, now Archichthys 

 (Strepsodus) Portlocki. 



