CTENODONTA PENTONENSIS. 139 



Nucula ? cuneata. Phillips, 1836. 



Nucula ? cuneata, Phillips, 1836. Greol. Yorks., vol. ii, p. 210, pi. v, fig. 14. 



Specific characters. — Shell transversely elongate, cuneiform, equivalve, very 

 inequilateral. Anterior end small and almost sharp. Posterior end slightly 

 expanded and compressed, its border bluntly rounded. Superior and inferior 

 margins subparallel. Umbones small, placed very far forwards, a well-marked 

 broad escutcheon. 



Interior. — Details not obvious. 



Exterior. — Surface is ornamented with almost obsolete parallel lines and striae 

 of growth. 



Dimensions. — 



Antero-posteriorly . . . .10 mm. 



Dorso-ventrally . . . .9 mm. 



Locality. — Bolland, Yorkshire. 



Observations. — I am unable to determine the real generic affinities of this shell. 

 But it is necessary to retain the species, still doubtfully referred to Nucula, as the 

 specimen is preserved in the Gilbertson Collection of the Natural History Museum, 

 South Kensington. I do not think that it belongs to Nucula, and it is to be hoped 

 that eventually more specimens will be found. The locality of Bolland is so vague 

 that it is impossible to say exactly where or at what horizon the shell occurred. 



Ctenodonta pentonensis, Hind, 1899. Plate XXII, Figs. 4 — 7. 



Ctenodonta pentonensis, Mind, 1899. Quart. Journ. Geol. Soc, vol. lv, p. 369, 



pi. xxv, figs. 1 — 3, 3a, and 4. 



Specific Characters. — Shell transversely and triangularly ovate-acute, moderately 

 gibbose, very inequilateral. 



The anterior portion of the shell is about one-third of the valve, and is 

 moderately swollen, its border being elliptically curved. The inferior border is 

 extended, and is very convex. The posterior border is exceedingly small and 

 bluntly pointed, much narrowed by the approximation of the upper and lower 

 borders. The hinge-line is arched, especially in front, but becomes straight, 

 extended, and depressed posteriorly. 



The umbones are moderately swollen, incurved, contiguous, elevated, forming 

 the highest point of the shell, and excavated in front, but there is no real hmule. 



