ANTHRACOMYA MODIOLARIS. 97 
_ Whitley, Newcastle and Durham Coal-field; Grain’s Ironstone, South Stafford- 
shire; Stubb’s Mine, Bardsley. South Wales Coal-field: Sychffos; Darren Pins, 
Aberdare. Scotland: Splint Coal, Shettleston, Ardrie, and Larkhall; Annandale, 
Kilmarnock, Old Cummock, Ayrshire,—all in the Upper and Middle Coal-measures. 
Observations.—Owing to the fortunate preservation of the types of this shell 
and the specimen subsequently figured by Salter, I have been able to reproduce 
them by the kindness of Prof. Prestwich and of Sir A. Geikie, Director-General 
of the Geological Survey, and with the exception of two synonyms invented by 
Captain Brown and a mistaken reference by myself this shell has always been 
recognised by authors. I figure these shells from Prof. Prestwich’s Coalbrookdale 
Collection on Plate XVI, figs. 49 and 50 representing the two specimens 
figured by Sowerby (op. cit. supra) as his fig. 10. I judge from measurements, 
and from the fact that Prof. Prestwich has marked both specimens as figured, that 
the two figures numbered 10 in the ‘Geology of Coalbrookdale’ are from 
different specimens, one showing the view from above, the other and larger one 
from the side. These are both more elongate than Mr. Salter’s form, and have 
the dorsal and ventral margins more nearly parallel; but with these in Prof. 
Prestwich’s Collection is a shell from the same locality figured on Pl. XVI, 
fig. 51, which is almost identical in form with Mr. Salter’s shell, showing that in the 
young the shell had a more triangular shape. I produce on PI. XIII, fig. 9, the 
shell which was the original of Mr. Salter’s figure in the ‘Geological Survey 
Memoir on the Iron Ores of South Wales.’ This is also a cast, but it shows no 
muscle-scars, except the anterior adductor very faintly on the left side. 
From the series figured from North Staffordshire it will be seen that the 
shape and degree of acuteness of the oblique ridge is very variable, and also the 
- amount of expansion upwards of the posterior part of the hinge-line. This may, 
I think, be due to the fact that the types are all casts, and that the thin part of 
the valves which came absolutely into contact with each other would therefore not 
be indicated in casts. All the shells, it may be noted, which have this character 
possess more or less shell-structure preserved. Thus fig. 10, Pl. XIII, and 
figs. 1, 7, and 8, Pl. XIV, all show the posterior part of the hinge-line expanded 
upwards. 
I have been fortunate enough to obtain a nearly perfect example of the hinge 
of this species, only the extreme anterior and posterior positions being wanting. 
This specimen, which is figured on Pl. XVI, fig. 52, came from the same bed at 
Whitley, Northumberland, where Prof. King obtained the hinge-plates on which 
he founded his genus Anthracosia, and shows a characteristic posterior lateral 
tooth, and a small cavity under the umbo, probably to receive a cardinal tooth of 
the opposite valve. 
Whether these conditions obtain in other species is at present unknown. 
13 
