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 striae of any kind. 

 Assuming this cylindrical state to be the true character of the shell, it resembles that 

 section of the genus called Lithodomus, 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 M. angmta, Desh. (Coq. foss. des Env. de Par., 

 t 1, p. 266, pi. 41, figs. 6 — 8), but it differs in having the umbo terminal, and our shell is 

 much more unequally tumid. The locality is unfortunately not known. 



20. Modiola undulata, S. Wood. Tab. XIII, fig. 13, a, b. 



Spec. Char. 31. testa tenui, deprcssd, elongato-cuneatd ; sip/ioni-rer/ione latiore, de- 

 pressd ; exttis laevigata, undulata. 



Shell thin, depressed, elongately wedge-shaped ; siphonal region broad, depressed ; 

 externally smooth, and undulating. 



Lengtli, 2 inches. 



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 Modiola, 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 I am acquainted with. The undulations of the exterior do not look as if 

 they could have been produced by compression or accident. 



The entire figure [b) 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 HighclifT, Barton, and is in Mr. Edwards's 

 cabinet. The striae, or rather costs 1 , 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 striae 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. 



