HIGHEST BEDS OF THE DURHAM COAL MEASURES. 223 
or less ovate or oval, flatly convex or patelliform, and with a sort 
of blunt, reflexed apex or umbo eccentrically placed near one ex- 
tremity. The shell is extremely delicate and more or lessirregularly 
wrinkled by compression; but besides the wrinkles due to this 
cause, the surface is ornamented by a series of regular, concentric 
ridges or plaits, which have the umbo for their centre. This is 
the general character of the fossil when seen congregated in 
groups on the plane surfaces of the ironstone. But on closely 
examining isolated individuals in other parts of the matrix, so 
as to see clearly the true marginal outline, we perceive that one 
part of the margin is straight—as though it were a hinge line, 
and that the apex or umbo is more decidedly eccentric than the 
congregated specimens appear to show. Examples from the 
shale, which occur as extremely delicate, black, occasionally 
iridescent films, also show with great clearness the straight 
border and eccentric umbo, as well as the features previously 
mentioned. 
It is the last named characters—the straight margin and 
eccentric umbo that give to this fossil its strong resemblance to 
Estheria. And it is these that cause me still to have a sort of 
half belief in my old opinion. But as this is contrary to the 
views of Professor Jones, who possesses a thorough knowledge of 
the Estherie both fossil and recent, I feel satisfied I must be 
wrong. On the other hand I do not think it is a Discina, on 
account of its straight border and eccentric umbo. ‘The vege- 
table remains with which it is associated also oppose the 
idea of its being a marine shell. For the present, therefore, it 
will be as well perhaps to retain as a provisional name, Pro- 
fessor Phillips’ term of Ancylus. This I propose, chiefly to get 
rid of the evil of having an unnamed fossil—which perhaps is the 
next greatest evil to that of having a fossil with too many 
names—and not because I am of the opinion that it really 
belongs to Ancylus. For whether it be an entomostracan or a 
mollusc, the evidence certainly would appear to go towards 
proving that it had a bivalvular, rather than a univalvular 
carapace. ‘Taking for its specific name that of its original dis- 
coverer, Mr. Vint, I would describe it in the following words :— 
