160 EOCENE MOLLUSCA. 
a fulcrum. The dentition, also, in digitaria is different, there being in the right valve of 
that shell one cardinal obtuse and truly triangular tooth, and two elongated and distinct 
and distant lateral teeth, with a similar arrangement of denticles in the left or opposite 
valve, so that the prominent parts of the hinge of the one interlock into the corresponding 
depression of the other; but im the Eocene shells there are no lateral teeth, only one 
large bifid or diverging cardinal tooth—or, I ought rather to say, they are two distinct 
diverging teeth in the right valve beneath the umbo. There are no oblique markings 
upon the exterior of the older Tertiary shells—only crenulations upon the immer margins 
of the valves, which diverge or run out in opposite directions; but in digitaria those 
oblique markings are wholly confined to the outer layer of the shell, and are not 
impressed upon the inner margin,—corresponding in that respect with those species of 
Astarte in which the exterior is ornamented with oblique ridges. 
In the ‘ Journ. de Conch.,’ vol. x, p. 141, M. O. Semper has enumerated nine species 
as belonging to this genus; and these he has divided into three groups, viz., Ist, espéces 
strieés, four species ; 2ndly, especes lisses, four species; and 3rdly, espéces inéquilatérales, 
surface striée ott treillissée. “With the exception of digitaria, Limn., they are all fossil. 
1. Woopi1a crenuLata? Deshayes. ‘Tab. XXV, fig. 11. 
Woopia cRENULATA (?), Desh. An. sans Vert. du Bass. de Par., t. i, p. 792, pl. lix, 
figs. 9—11, 1860. 
Spec. Char. “ W. Testé minima, orbiculari, solidula, conveaiuscula, levigata, sub- 
aquilaterali ; umbonibus tumidulis, oppositis ; marginibus lateralibus late et oblique crenu- 
latis, margine inferiore tenuissime crenulato, dente cardinali unico in valvula dextra postice 
elongato ; dentibus duobus in valvuld sinistra subequalibus.” —Deshayes. 
Shell small, orbicular, strong, slightly convex, smooth, nearly equilateral ; umbones 
slightly prominent, inner margins broadly and obliquely crenulated; one cardinal tooth 
in the right valve, and two diverging teeth in the left. 
Diameter, 3th of an inch. 
Locality. Barton (Ldwards). 
A single specimen of this genus is all that I have seen from the English Lower 
Tertiaries ; it is in Mr. Edwards’s cabinet, and it has affixed to it the MS. name of 
W. orbicularis, from which I presume that gentleman considers it to differ from the 
French shell. I feel unwilling, however, to found a new species upon the minor 
differences here presented ; and it will require a comparison with the type specimen of 
M. Deshayes before a separation could be justified, and this I am not able to make. 
Our specimen is the right valve, and the cardinal “bifid denticule” is, in fact, composed 
of two teeth, diverging from beneath the umbo at an angle of 75°. These teeth are of 
unequal size and length, with a distinct separation between them: there are no lateral 
