74 EOCENE MOLLUSCA. 
specimens are unfortunately not very perfect, but a portion of the shell is visible on one 
of them; this appears to have been quite smooth and free from striz of any kind. 
Assuming this cylindrical state to be the true character of the shell, it resembles that 
section of the genus called Zithodomus, but whether this form be produced from a con- 
fined position it is difficult to say. Unlike the generality of the cylindrical species, the 
siphonal region of our shell, if not distorted, is much compressed, and the margins are 
quite closed. 
This species somewhat resembles JZ. angusta, Desh. (Coq. foss. des Env. de Par., 
t. 1, p. 266, pl. 41, figs. 6B—8), but it differs in having the umbo terminal, and our shell is 
much more unequally tumid. ‘The locality is unfortunately not known. 
20. Moprona unpuuata, S. Wood. Tab. XIII, fig. 13, a, 3b. 
Svec. Char. M. testé tenui, depressd, elongato-cuneatd ; siphoni-regione latiore, de- 
pressd ; eaxtus levigatd, undulata. 
Shell thin, depressed, elongately wedge-shaped; siphonal region broad, depressed ; 
externally smooth, and undulating. 
Length, 2 mches. 
Localities. Harwich and Bawdsey. 
There are two specimens of Septaria in the Museum of the Geological Society, 
marked respectively Nos. 8290 and 15314, presented by the Rev. J. Holmes, to which 
are attached the above localities ; they bear the impressions and the greater part of the 
shell of a few specimens of a species of AZodio/a, but in a compressed and mutilated con- 
dition ; they are, however, sufficiently perfect to show, by their lines of growth, that they 
most probably belonged to a species quite distinct from any other Eocene form, or at least 
from any that Iam acquainted with. ‘The undulations of the exterior do not look as if 
they could have been produced by compression or accident. 
The entire figure (4) is a restoration. 
Tab. X, fig. 5, represents the fragment of a shell which appears to belong to this genus, 
and the ornamentation is so peculiar that I think it deserves to be represented in order to 
call attention to its existence. It is from Highcliff, Barton, and is in Mr. Edwards’s 
cabinet. The striz, or rather coste, which cover the dorsal portion of the siphonal 
region, are few and very large, differing from those upon the other part of the shell, from 
which character it might be called diversa. Some species have the strize of the same 
magnitude all over the surface, in others the striae are smaller or narrower on the dorsal 
portion of the siphonal region, and this diversity is, I think, a good mark of distinction. 
