CARBONICOLA OVALIS. 57 
Specific Characters—Transversely oval with rounded ends; the umbones are 
more central than in C. acuta, and the inferior border is regularly curved, having 
a convex outline. This curve passes gradually into the anterior and posterior 
borders, so that the anterior and posterior ends are both regularly rounded. 
Interior—as in Carbonicola acuta. Exterior—striz and lines of growth con- 
centric. 
Dimensions, Sowerby’s type of Unio centralis : 
Antero-posteriorly  . : : . 35°5 mm. 
Dorso-ventrally ‘ ‘ : . 23°5 mm. 
Laterally . . - 5" tim, 
Observations—This somewhat infrequent form I regard as closely allied 
to C. acuta. Indeed, had it not been for the fact that Martin figured and 
described the shell, I should probably have considered the form as ©. acuta. It 
occurs occasionally in the C.-acuta-bed of North Staffordshire (Cockshead roof). 
Sowerby, in his ‘ Mineral Conchology,’ substituted the name Unio wniformis for 
Martin’s A. ovalis, for reasons of nomenclature; but the shell which he described 
is said to have come from Felmersham, in Bedfordshire, and is therefore an 
Oolitic species, and not in any way related to Martin’s form, which was from the 
ironstone of Tupton Moor and Staveley. Martin’s original specimen has 
disappeared, but it had the characteristically curved lower border rounded off 
anteriorly and posteriorly. Martin describes ‘‘ one end pointed,” but the figure 
shows for the posterior end a different shape from the ordinary form of 
CO. acuta. 
I regard Sowerby’s form of Unio centralis, from Coalbrookdale, ple xexxix, 
fig. 13, in Prof. Prestwich’s memoir, as identical with Martin’s species, and I have 
been permitted, by the kindness of Prof. Prestwich, to re-figure the original 
specimen, Pl. IV, fig. 18. This specimen shows umbones more central than 
usual, but this is due to some imperfection of the posterior end. PI. IV, fig. 19, 
is a cast of another specimen from the same locality, and is in the Nottingham 
Museum. One other specimen from the same collection is in Pl. IV, fig. 22, 
from Butterley, Leicestershire. Pl. IV, figs. 20 and 21, are forms lent me by 
Mr. J. Neilson from the Kenmuir and Clydesdale pits near Glasgow, the latter of 
which shows a form intermediate between C. acuta and C. ovalis. 
Salter’s figure of Anthracosia ovalis in the ‘ Geological Survey Memoir on the 
Tron Ores of Great Britain,’ part 3, pl. 1, fig. 22, is, I think, that of a totally 
different shell, viz. Carbonicola turgida. The hinge-characters are shown on 
Pl. V, fig. 38, in a specimen which I obtained from the Cockshead rock, which 
lies some little way above the Cockshead Bass (the C.-acuta-bed). 
It has the form y, which I have described above under C. acuta: thus in the 
right valve a central subumbonal tooth, with concavity anterior and posterior to 
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