90 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 
shell figured are from the Little Mine ironstone of Great Fenton Colliery, and 
may be regarded as typical of the various forms which the shell was capable of 
assuming. The chief points to be noted are the differences in the comparative 
measurements, and in the shape of the posterior end, which becomes in some 
specimens almost square (Pl. XII, figs. 6 and 9). 
In my paper (‘ Quart. Journ. Geol. Soc.,’ vol. xlix, 1893, p. 260) I made the 
statement that the left valve was slightly more convex than the right, a fact which 
I now believe to have been due to some slight dislocation of the valves after death, 
for the examination of a larger number of specimens has convinced me that this 
character was only accidentally present. Mr. Salter stated that the right valve 
was more convex. I have seen very few specimens indeed which afford any 
indications of the hinge or interior. Fig. 3, Pl. XII, however, shows a very thin 
hinge-line; and fig. 4, Pl. XII, is a cast of the hinge and part of the interior. 
The line which indicates in this specimen the junction of the valves is perfectly 
straight, and exhibits no flexures. In front, too, are seen on either side the 
accessory adductor muscle-scars, which unfortunately the artist has not indicated 
quite strongly enough. Some specimens (Pl. XII, figs. 3 and 10) show well- 
marked colour-bands. 
Mr. Salter (op. supra cit.), in his remarks on this species, says, ‘‘ A very much 
compressed species, with the look of a smooth Myacites—to which, in fact, it is 
allied ;” but he does not go any further into details. The type specimen is 
somewhat smaller than the majority of those figured on Pl. XII, and has the 
subtruncate posterior end of figs. 6, 9, and 12. 
Mr. Salter states that the ‘‘ epidermis is moderately wrinkled in front, much 
so posteriorly ;” but this is not a constant fact, the opposite condition obtaining in 
fie. 17, Pl. XII, and in fig. 19, Pl. XII, the greatest amount of wrinkling being 
over the central part of the shell, and the position is evidently quite accidental. 
With regard to the change of shape due to growth, I have figured what I take to 
be young forms, Pl. XII, figs. 14, 15, 16, and 13. Fig. 14 indicates the very 
young state, and this form occurs in large quantities with even smaller specimens, 
as a sort of spat bed in the Burnwood ironstone shale of Goldenhill. Figs. 13, 15, 
and 16 are from the same bed as the larger specimens. From a study of these it 
would appear that the posterior part of the shell enlarges with age at a greater 
rate than the anterior end, and a similar condition of growth obtains in other 
species of the genus. The adult form of this shell is by far the largest of all the 
species of this genus, and though occurring plentifully locally it is only found in 
the Soap vein of Pen-y-cae, South Wales Coal-field, and the Burnwood ironstone 
and black shale immediately above it, in the North Staffordshire Coal-field.' I 
1 In ‘ Geol. Surv. Mem. Iron Ores of Great Britain, part 4, p. 294, A. Adamsii is stated to have 
been obtained with A. pumila and A. centralis from the Knowles Shale of Fenton and Longton, but I 
