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 Garbonicola acuta. Exterior — striae and lines of growth con- 

 centric. 



Dimensions, Sowerby's type of TJnio centralis : 



Antero-posteriorly .... 35*5 mm. 

 Dorso-ventrally .... 23 - 5 mm. 



Laterally . . . . .15 mm. 



Observations. — This somewhat infrequent form I regard as closely allied 

 to G. acuta. Indeed, had it not been for the fact that Martin figured and 

 described the shell, I should probably have considered the form as C. acuta. It 

 occurs occasionally in the G.-acuta-bed of North Staffordshire (Cockshead roof). 



Sowerby, in his ' Mineral Conchology,' substituted the name TJnio uniformis 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 

 G. acuta. 



I regard Sowerby's form of Unio centralis, from Coalbrookdale, pi. xxxix, 

 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, PI. 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 PI. IV, fig. 22, 

 from Butterley, Leicestershire. PI. 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 G. acuta and G. ovalis. 



Salter's figure of Anthracosia ovalis in the ' Geological Survey Memoir on the 

 Iron Ores of Great Britain,' part 3, pi. ii, fig. 22, is, I think, that of a totally 

 different shell, viz. Garbonicola turgida. The hinge-characters are shown on 

 PI. V, fig. 38, in a specimen which I obtained from the Cockshead rock, which 

 lies some little way above the Cockshead Bass (the G.-acuta-bed). 



It has the form y, which I have described above under G. acuta : thus in the 

 right valve a central subumbonal tooth, with concavity anterior and posterior to 



8 



