CARBONICOLA ACUTA. 53 
Bowling Alley, over Four-foot Coal, Wetley Moor; N. Staffs Coal-field; above the 
Broach Coal, Dudley; Middle Coal-measures of Bolton, Bury, and Oldham; Coal- 
measures, Nottingham; Unston, Derbyshire. South Wales: Rosser Vein, Cwm 
Bryn ddu, Jack mine, Cwm Aman. Blue Vein, Gantre; Bottom Vein, Sirhony. 
Stanley Main; Wakefield; Sheden; Lowmoor, Middleton; Band, near Townelly 
Seam, West Wylam. Eltingham Colliery, Prudloe; Northumberland and Durham 
Coal-field. Scotland: Kilmarnock; Shotts; Airdrie, Shettleston, U.C.-m.; Hight- 
foot Coal, Scoonie ; roof of Hight-foot Seam, Durie Colliery ; Fifeshire Coal-field. 
Observations.—This species has a wide distribution, both horizontally and 
vertically. Its form, however, as might have been expected, varies considerably. 
The type form (Sow.), Pl. III, fig. 1,is perhaps the most common, but the varieties 
do not seem to be due to local or horizontal environment. I find them all occurring 
in numbers in the roof of the Cockshead Seam of the North-Staffordshire Coal- 
field, with members of an intermediate form, indicating the lines of variation. In 
many specimens there exists a feature denied to this species by M‘Coy, namely, a 
subconstriction or oblique sulcus, widening as it approaches the ventral border, 
and showing a close relationship to similar forms of C. robusta, with the smaller 
elongated form of which shell, indeed, C. acuta is closely allied, differing chiefly 
in the relatively smaller dorso-ventral and lateral measurements. 
M‘Coy relied on “ the lengthened form, straight insinuate ventral margin, the 
side without any oblique concavity, . . . . . aswellas the greatest width [dorso- 
ventral] being a little behind the beak, instead of from the apices,” as charac- 
teristics of this species ; yet, while many shells agree with this description, one or 
other of these characters often varies. 
I think, with M‘Coy, that the forms described and figured by Brown (op. cit. 
supra) as Pachyodon, and Unio exoletus, antiquus, transversus, and Levidensis, are 
forms of this species; and to these I would add the forms Pachyodon and Unio 
agrestis ; but it is impossible to judge accurately from drawings only, and the 
original specimens have entirely disappeared. Yet, from other localities, I know 
examples of these forms which I consider to belong to this species. 
I am disposed to regard, from inspection of the figures and Goldfuss’s descrip- 
tion, Unio tellinarius as an example of this species. De Koninck appears to have 
copied Goldfuss’s figure, but it is difficult to be certain as to identification, as 
the original specimens have disappeared. 
M‘Coy thought that his Carbonicola subconstricta was synonymous with the Unio 
and Pachyodon tellinarius of the above authors. 
Fleming has curiously enough (‘ History of British Animals,’ p. 417, 1828) 
referred Unio acutus, Sowerby, to the Middle Oolite ; but this must be an error, 
for Sowerby gives “ Bradford,” Yorkshire, as the locality of this shell. 
I have been permitted by the kindness of Dr. H. Woodward to figure the 
