BIVALVIA. 71 
This is an extremely delicate shell, and very rare; a few specimens, however, are 
quite perfect, and will bear a fair comparison. The shell to which it most nearly 
approaches is the common British species, 17. marmorata, but it differs essentially in several 
characters; these have been pointed out by M. Deshayes, the founder of the present 
species. The British fossil appears to correspond with the French shell, so far as depen- 
dence can be placed upon figures and descriptions, and I have not been able to see a 
specimen of the latter. The strize on the pedal region are very large or broad, becoming 
narrower towards the central smooth space, where they terminate with two or three very 
fine lines; the radiations on the siphonal region are not so broad; all the rays are flat, 
with narrow depressions between them. The smooth or naked central space occupies 
about one third of the surface of the shell, and the lines of growth are here distinctly 
visible, sometimes raised almost to ridges. The rays on both regions of the French shell 
are represented of the same size, but they are not so on ours. 
One of Mr. Edwards’s specimens has enclosed within its valves no less than three 
others, enveloping one another; one of these enveloped specimens is in a reversed 
position. 
15. Moptoza simpiex, J. Sowerby. Tab. XII, fig. 7, a, 0. 
Moptota stmpLex. J. Sow., in Dixon’s Geol. of Suss., pp. 117, 225, t. 14, fig. 16, 1850 
= _ Morris. Catal. Brit. Foss., p. 212, 1854. 
Spec. Char. M. testa tenui, elongata, obtuse cuneata vel subtrapeziformi, levigald ; 
umbonibus minutis, depressis, subterminalibus ; pedi-regione brevi, contractd ; siphoni- 
regione latiore, compressa ; margine dorsali recta, eatensd. 
Shell thin, elongated, obtusely wedge-shaped or obtusely trapeziform, smooth : 
beaks small, depressed, nearly terminal; pedal region very small and narrow ; siphonal 
region broad and compressed ; dorsal margin straight and extended. 
Length, \2 inch. 
Localities. Bognor and Herne Bay (dwards). 
Mr. Sowerby says, “It is like J/. depressa of ‘Min. Conch.” but is more pointed.” 
There appears also to be a little difference in outline ; the dorsal margin is less curved 
and more extended, and the siphonal region is rather more compressed. 
16. Moptoxa suscarinata, Lamarck. 'Tab. XII, fig. 9. 
Moptora supcartnata. Lam. Ann. du Mus, t. vi, p. 222; and t. ix, pl. 17, fig. 10a, 0. 
— — J. Sowerby. Min. Conch., pl. 210, fig. 1, 1818. 
_ — Desh. Coq. Foss. des Envy. de Par., t. i, p. 256, pl. 39, figs. 4, 5. 
— — Morris. Catal. Brit. Foss., p, 212, 1854. 
— — Desh. An. s. Vert. du Bassin de Par., t. il, p. 25, 1860. 
Mytrius — D Archiac. Foss. du gr. numm. dans Mém. de la Soc. Géol. de 
Fr., 2 sér., t. ili, pp. 433, 453, 1850.’ 
