66 EOCENE MOLLUSCA. 



in some degree accidental. The striae 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 

 Bracldesham 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 

 ^he 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 a 

 looks like a distortion. 



0. Modiola eximia, S. Wood. PI. XIII, fig. 6, a, b. 



Spec. Char. M. testa minima, ovato-ellipticd, obliqud, valde inaquilaterali, pedi-regione 

 bred, ro/undatd; siphoni-regione latiore ; spatio submediano parvo, Icevigato ; striis tenu- 

 ibus, exilissimis ; n/argine venfrali arcuato. 



Shell small, ovately elliptical, oblique, very inequilateral ; pedal region small, short, and 

 rounded; siphonal region broader; central region free from stria 1 , ventral margin rounded. 



Length, ^th of an inch. 



Locality. Highcliff, Barton {Edwards). 



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 stria: 1 

 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. 



