BIVALVIA. 73 
form, as well as possessing a linear series of denticles, seem to point out its place 
as near to Nucula from which it differs essentially, in having an external ligament, 
and one large lateral tooth upon the anterior side. 
The shell is of a nacreous texture within, and was, probably, covered with an 
epidermis in the recent state. The ligament is placed on the posterior side of the 
umbo, upon a small projecting portion of the shell, and the animal was without 
prolonged siphonal tubes, the line impressed by the edge of the mantle being like 
that of Nucula, without any indentation. There are no recent species, that I am 
acquainted with, possessing such a dental arrangement, and its true position is of 
course conjectural. The linear teeth and external ligament resemble Pectwnculus, with 
a form like that of Mucula. 
1. NucINELLA miILiARtIs, Deshayes. Tab. X, fig. 4, a—c. 
Nucuta minraris. Desh. Coq. Foss. des Env. de Par., tom. i, p. 225, pl. 36, figs. 7-9, 
1829. 
Pievuropon ovatts. SS. Wood. Illust. in Mag. Nat. Hist., 2d Series, vol. iv, p. 231, pl. 13, 
fig. 1, 1840. 
—_ MILIARIS. S. Wood. Catalogue, 1840. 
Spec. Char. Testé minima, subovatd, levigatd, politd, tumidd ; posticé subtruncatd, 
antice productiore, rotundato-ovatd : dentibus 5—6 magnis, obtusis. 
Shell minute, subovate, smooth, glossy, and tumid; posterior side short, subtrun- 
cate, anterior large, roundedly ovate; teeth 5—6, large and obtuse. 
Diameter, 3, of an inch. 
Locality. Paris Basin, Grignon. 
Cor. Crag, Ramsholt, and Sutton. 
This pretty little shell is by no means rare at either of the above British localities, 
and at the former (Ramsholt), the valves are often found united, the large and pro- 
minent teeth with which they are furnished having kept them in their natural position. 
It is one of the very few of our Crag Molluscs, that dates its existence from the 
Older Tertiaries, or what is called the Eocene Period; as there is reason to believe 
the species left in the Paris Basin is the true progenitor of our little shell, while it 
appears to have died out before the severer conditions of the Red Crag Period had set 
in: although so small a shell, it would not readily be found, unless abundant, in a 
deposit so disturbed. 
As, however, some differences exist between the Crag Fossil, and what is here 
considered its specific parent, it may be necessary to give a more detailed description 
- and to point out what, perhaps, might be regarded by some Conchologists as of 
sufficient importance to keep them distinct. 
Our little shell in its outward form, slightly resembles a minute specimen of 
Nucula nucleus, except, that it is more tumid; the anterior side constitutes nearly 
the whole of the shell, the posterior being cut off by an almost straight line from the 
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