92 CARBONICOLA, ANTHRACOMYA, AND NATADITES. 
Specific Characters.—Shell obliquely subquadrate, compressed, and expanded. 
Umbones obtuse, much nearer the anterior end than in A. Adamsii. The anterior 
end is almost obsolete and very obtuse, on which account the oblique sinus is 
absent. The diagonal swelling is broad, and not well differentiated from the rest 
of the shell. The anterior, inferior, and posterior borders form part of one 
general curve, which meets the inferior border posteriorly at an obtuse angle. 
There is no relic of a byssal notch. In other points the shell agrees with the 
general description of A. Adamsii. 
Dimensions (Pl. XIII, fig. 9) : 
Antero-posteriorly ; . 5 . Od mm. 
Dorso-ventrally : : . . 42 mm. 
Laterally . : 5 - So mm, 
Localities —The same beds in the North Staffordshire Coal-field in which 
A. Adamsti occurs. 
Observations.—From the description and figure in the ‘ Geology of Coalbrook- 
dale’ of Unio dolabratus, at first sight it might be considered that the variety 
under description was referred to, but owing to an imperfect example a partly 
erroneous diagnosis was given. Salter, in his observations on A. Adamsii, says 
that A. dolabrata, Sow., may be distinguished by having an almost obsolete 
anterior end, but he did not notice the fact, well shown in the drawing, that the 
anterior end was incomplete through fracture. 
A, Adamsii, var. expansa, also differs from A. dolabrata in possessing a much 
less convex but more expanded form. Fig. 11, Pl. XII, is a form of intermediate 
character between A. Adamsii and the var. expansa. It possesses the general 
shape of the variety, but the position and shape of the umbones is very remarkable ; 
they are more posteriorly situated than in any other specimen of A. Adamsii that 
I have met with, and are at the same time more defined, more tumid, and raised 
to a greater height above the hinge-line. This shell is not crushed in any way, 
though it was split in two in extracting it from its ironstone matrix. A large 
crushed specimen of the variety ewpansa which I figured in my former paper came 
from the shale above the Burnwood ironstone at Pitts Hill, and measured 65 mm. in 
length, and 55 mm. in the dorso-ventral diameter. It may be noted that at Pitts 
Hill, Golden Hill, and Kidsgrove the top portion of the Burnwood ironstone differs 
hthologically and paleontologically from the lower part. The top part consists of 
thin lamine of brown and lighter coloured ironstone, passing up into a black shale, 
and containing Anthracomya Adamsii and its variety eapansa, and a lower more 
compact mass without marked lines of deposition, which contains Anthracomya 
pulchra and a small Naiadites, the two forms of Anthracomya never occurring 
together. On the other hand, at Great Fenton I cannot make out this sharp 
division, and have never seen A. pulchra in the bed at this place. 
