CARBONICOLA NUCULARIS. 63 
8. CARBONICOLA NUCULARIS, sp. nov. Plate VII, figs. 24—42; Plate IX, fig. 11; 
Plate XI, figs. 14 and 16. 
Specifie Characters.—Shell produced transversely in adults, moderately gibbous, 
evenly convex, more so comparatively in young forms. Anterior end short, about 
one-fourth of the whole shell, with a regularly curved border meeting the hinge- 
line above at an angle, but passing into the inferior border with a regular curve. 
Inferior border broadly curved in its anterior half; then becoming straight and 
slightly sinuous. Posterior border bluntly rounded ; in older forms the junction 
with the inferior border is somewhat angular. Hinge-line apparently slightly 
arched, due to the meeting of the anterior and posterior parts at an obtuse angle. 
The posterior end is regularly and evenly compressed into its lower and posterior 
borders; but above the posterior-dorsal slope is expanded, subcarinate, and slightly 
concave above. Umbones obtuse and blunt, remote, varying slightly in position, 
never central, somewhat raised above the hinge-line; lunule small. Hinge-plate 
narrow ; the anterior and posterior parts meet at a very wide angle. In the right 
valve there is a small cardinal tooth just posterior to the umbo, with a pit behind 
it, Pl. IX, fig. 11. The posterior part of the plate is a narrow ledge, with a groove 
above it for the ligament. Interior normal. Internal surface very smooth, marked 
on the posterior slope by radiating lines. 
Surface in the two testiferous forms marked with very faint concentric lines 
of growth. Periostracum much wrinkled. 
Measurements : 
Antero-posteriorly. Dorso-ventrally. Laterally. 
28 mm. 17 mm. 11°5 mm. 
Medium forms 20 ,, V4" s; Ow 55 
Young forms 16 ,, (Pay es 9° =, 
Localities —England : Hard-mine roof, North Staffordshire. Mountain Mine, 
Wigan. Doe Hill, Nottingham. Leicester Coal-field. Coal-measures, South 
Wales. Scotland: Limestone-Shale, Dunfermline. 
Remarks.—There is some resemblance between the species under description 
and the figure given by Mr. R. Etheridge, jun., in the ‘ Quart. Journ. Geol. Soc.,’ 
vol. xxxiv, pl. ii, fig. 20, under the name of Anthracosia ? nucleus (Brown ?), but 
he states that the specimen was too imperfect to give a description of it. It was 
from the original locality of Captain Brown’s Unio and Pachyodon nucleus, the 
description of which differs only from my form in the fact that it is said to possess 
a posterior end elongated and acute, whereas I have never found a specimen which 
can be considered to be acute. Mr. Etheridge, jun., considered it probable that 
Brown’s shell was identical with one form of Rhind’s Awinws Pentlandicus, ‘ Age 
