CARBONICOLA ANTIQUA. 79 
obtuse angle with the upper border; it then becomes rapidly rounded, the 
convexity being very acute at the junction with the inferior border, which is 
sinuously curved, so that the posterior inferior angle of the shell, which is very 
blunt, is below the level of the rest of the border. The posterior border is 
convexly truncate. There is a marked shallow, oblique subconstriction, which 
does not extend far up the shell towards the posterior end. The shell is much 
broader at its upper border than anywhere else. The umbones are anterior, 
broad, obtuse, and remote, rising rapidly in front, and posteriorly forming an 
acute well-marked ridge, which passes down towards the inferior angle, just 
above which it becomes lost on the surface of the shell. 
The posterior part of the shell above this ridge is deeply channelled, the 
groove becoming wider and shallower as it passes backwards. The lunule is wide 
and flattened. The posterior ligament appears to be attached to the faces of the 
hinge-plate. 
Interior normal. Exterior: Lines of growth very fine. 
Dimensions : 
Antero-posteriorly : : : = idmm: 
Dorso-ventrally ; 4 E all Ommam,: 
Laterally : : . §mm. 
Locality. —Roof of the Hardmine Coal, Bucknall Colliery, North Staffordshire. 
Observations.—I kuow only two specimens of this species. They are totally 
different in shape and appearance from any of the other species, and loth as I 
am to found a species on the occurrence of only two examples in such a variable 
genus, I have felt that it was impossible to refer the shell to any known form. 
16. CarBoNicoLa ANTIQUA, sp. nov. Plate XI, figs. 28—30. 
Specific Characters.—Shell moderately tumid, nuculiform, oblique. The 
anterior end is short and swollen, with an almost circular border. The inferior 
border is gently convex in front, becoming straight in the posterior two-thirds. 
Its posterior surface is gradually compressed, with a bluntly truncate end, which 
may become almost pointed at the inferior angle; the descent of the superior 
border is at first somewhat rapid, it is flattened above, and terminates outwards 
in a bluntly rounded ridge which is continuous with the umbo above, and passes 
downwards and backwards to the posterior inferior angle. The umbones are 
anterior, depressed, moderately convex, pointed forwards and contiguous. 
Lunule is well marked and striated. The surface is ornamented with well-marked 
but fine lines and striz of growth, somewhat oblique in direction to the long axis 
of the shell. 
