102 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 
I had the opportunity, for which I thank Professor Geinitz, of examining the 
originals of his Anthracosia Weissiana, from the Saarbriicke Coal-field in the 
Dresden museum (op. supra cit.), and have no hesitation in referring that shell 
to the British form. Achepol’s Anthracosia Harz, from the Hannebal group 
Bochum, is doubtless the same shell; and, if I am correct in my surmise that the 
Russian form is also identical, it is interesting thus to trace the shell right across 
Europe. 
Judging from the description of Plewrophorus subcostatus of Messrs. Meek and 
Worthen, I think it highly probable that their shell belongs to the species under 
discussion. I have quoted from their description antea, p. 87, to show that they 
lay stress on some of the characters which I consider typical of Anthracomya. It 
is said to occur in the Upper Coal-measures of Gallatin County, Illinois. 
The Anthracosia Harzi of Achepol is, I think, a specimen of A. Williamsoni ; 
curiously enough, this shell is not figured in the body of the work as a photograph, 
but is only in a supplement, which consists of a series of engraved figures of the 
shells previously described, but it is not stated if the shells are drawn from real 
specimens or are from restorations, and intended to give a general indication 
of the size and shape. 
Anthracomya Williamsoni varies very much in the shape of the posterior end 
and in its comparative measurements. At times the posterior border is truncate, 
at others bluntly rounded, or the inferior angle may be at times somewhat prolonged, 
so that it may become a right angle or even slightly acute. Many specimens show 
a typically gaping posterior end, and as many, on the other hand, have the valves 
close all round. I have not been able to satisfy myself that there has been any 
dislocation of the valves or eversion of the shell due to pressure or injury in those 
specimens which gape, and am inclined to believe that in some individuals the 
valves gaped and in others the valves were closed. The same conditions are to 
be observed in the marine fossil Sanguwinolites (?) sulcata, the Sanguinolaria sulcata 
of Phillips, from the Redesdale ironstone, some specimens of which shell appear 
to have widely gaping posterior ends, and others to be closed all round. 
In my notes made at the Natural History Museum of Brussels I have it that 
the specimen labelled there Mytilus prepes, de Ryckholt, is the same species as 
A. Williamsoni. The original drawing does not, however, show a very close 
resemblance, but the description is fairly characteristic. The original specimen 
was from the coal shale of Mons, the one I saw was from Longchamps. 
