66 EOCENE MOLLUSCA. 
in some degree accidental. ‘The stria on the siphonal region of the shell extend over 
more than half the surface, and those upon the pedal region are few and faint, sometimes 
obsolete. Mr. Sowerby speaks of a denticulated margin and a dentated hinge (note, p. 32, 
Min. Conch.), and says that it is very abundant at Highgate. In the specimens from 
Bracklesham the ridges or rays are small, with broad interspaces; in those from High- 
gate the ridges are about the same breadth as the interspaces ; those from Bramshaw have 
broad, flat ridges, with only narrow lines of separation, the Highgate specimens being 
intermediate. Casts of this or of some proximate species found at Harwich are in the 
Museum of the Geological Society. 
There are three different forms which I have figured, considering them all to belong to 
the same species, from my inability to draw a line of distinction between them. Among 
the Highgate specimens elongated as well as abbreviated specimens may be seen ; fig. 5 @ 
looks like a distortion. 
6. Moprona pxiurs, 8. Wood. Pl. XIII, fig. 6, a, 6. 
Spec. Char. M. testa minimd, ovato-elliptica, obliqud, valde inequilaterah, pedi-regione 
brevi, rotundatd ; siphoni-regione latiore ; spatio submediano parvo, levigato ; striis tenu- 
thus, evilissimis ; margine ventrali arcuato. 
Shell small, ovately elliptical, oblique, very inequilateral ; pedal region small, short, and 
rounded; siphonal region broader ; central region free from striz, ventral margin rounded. 
Length, 3th of an inch. 
Locality. Highcliff, Barton (Zdwards). 
A specimen of each valve of this elegant little shell is in the cabinet of Mr. Edwards, 
and these are all that I have seen. I imagine them to be full grown, as the muscular 
markings are deeply seated; the anal adductor impression is large, of an ovate form, and 
situated a little beyond the hinge-line ; the one in the pedal region is about half the size, 
situated near the umbo; the two are connected by a distinct mantle-mark. The striae 
cover the surface of the shell, excepting a small space on the pedal side of the ventral 
region; this naked space occupies about one fourth of the surface, and it is less, com- 
paratively, than upon any of our larger species covered with this kind of ornament. 
This character more especially, as well as a difference in outline, will, I consider, dis- 
tinguish it from the fry or young of any other species with which it was associated. 
The inner margin of our shell is crenulated all round, excepting the small space in the 
ventral region; the crenulations on the pedal side are few and large. The umbo is 
moderately elevated, and the shell, for its size, appears to be strong. 
