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 . . . .17 mm. 



Dorso-ventrally . . . .10 mm. 



Laterally . . . . .8 mm. 



Locality. — Roof of the Hardmine Coal, Bucknall Colliery, North Staffordshire. 



Observations. — I know 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 striae of growth, somewhat oblique in direction to the long axis 

 of the shell. 



