102 EOCENE MOLLUSCA. 
strie or depressed riblets decussated by lines of growth ; hinge-area broad, with few teeth, 
lateral denticles striated. 
Diameter, 2 inches. 
Localities. Uerne Bay (Zdwards), Upnor (Prestwich). 
France: Les environs de Soissons, pres d’Etampes, &c. (Desh). 
The most distinguishing character in this species is a prominent or rather recurved 
umbo, somewhat resembling the beak of a Zeredratula, which, I presume, suggested the 
name to Lamarck. 
Fig. 10, Tab. XVI, represents a shell that was some years since obligingly given to me 
by Professor Morris, and it had the locality of Ilford attached to it, but that gentleman is 
now unable to state from what bed it was derived. It was accompanied by a Cytherea from 
the same locality, and this latter species I have smce obtained from the Woolwich beds 
underlying the London Clay, reached in a well-smking at Romford. There is therefore 
every probability that our specimen came from the same bed at Ilford. Iam unable to 
assign this specimen to any species known to me, unless it might perhaps be referred to 
brevirostris, but with which it does not strictly accord. P. polymorphus also much 
resembles it. 
A shell from the Paris Basin has been figured and described under the name P. pauci- 
dentatus (Desh.), ‘An. sans Vert. du Bass. de Par.,’ t. i, p. 852, pl. 73, f. 16, 17, which 
has the locality of Woolwich attached to the description. I have not been able to find 
any British specimen entitled to that distinction. 
LIMOPSIS, Sassz, 1827. 
Gen. Char. Shell orbicular or slightly oblique, convex or lenticular, equivalved, sub- 
equilateral, closed ; hinge with two slightly curved and slightly unequal series of projecting 
and interlocking teeth ; umbones distant; connexus ligamental, bipartite, one portion 
inserted in a triangular cavity immediately beneath the umbo ; impression of the mantle 
entire. 
The animal of one species of this genus (LZ. awrita) has lately been obtained in the 
seas of North Britain by Mr. Jeffreys, the account of which has been published in the ‘ Ann. 
and Mag. Nat. Hist.,’ 1862, and he says ‘the body is of a milk-white colour. The mantle 
is open at every part except behind; it has no folds or tubes, and its edges are thickened 
and furnished with papilliform glands. The foot is large in proportion to the rest of the 
body, and it is shaped like a tobacconist’s knife; it can, in all probability, form a suboval 
disc at the central portion, as in Pectunculus.” It so much resembles that genus that 
the only distinction on which a separation can be founded is the triangular fossette in the 
area for connexus, and this cannot be considered a very important one, as it is present 
upon the young shell of Pectunaculus decussatus. 
