110 EOCENE MOLLUSCA. 



truncated ; the slope filled by a large, pointed, nearly flat lunette, edge toothed ; impression 

 of the abductor muscles shallow." — (/. Sowerby). 



Length, 1 inch ; height, f ths of an inch. 



Localities. Highgate, Potter's Bar [Wetherell) ; Haverstock Hill {Edwards). 



This species was apparently covered by a thick epidermis, and the umbones have been 

 very much eroded. The anal region or corselet is well marked and flat, with a slight rise 

 in the centre, and covered only by lines of growth. The surface of the shell is smooth to 

 the unassisted eye, but it is covered with narrow, deep, radiating lines, making the rays 

 broad and flat, and there is a depression on the dorsal portion of the pedal region irre- 

 spective of the lanceolated lunule, as if the ventral margins were capable of being widely 

 separated. The species appears to be confined to the London Basin. 



The interior cast of a shell of this genus is figured and described in the ' Trans, of 

 the Geol. Soc.,' 2nd series, vol. v, pi. 24, fig. 5, under the name N. Baboensis, and is 

 said by the author to " nearly resemble N. Bowerbankii, but not truncated or pointed 

 below the lunette." This specimen came from Baboo Hill in Cutch, and it is in that 

 easterly direction that we might look, I think, for shells probably identical with some 

 of our own Eocene fossils, but I fear it is not possible to certify a species by the cast alone. 

 There is also the cast of a species in this genus found in the Eocene Formation, between 

 Holyport and Birfield ; the specimen was deposited in the Museum of the Geological 

 Society, by the late Mr. Warburton (marked No. 17839), and has a somewhat similar 

 form, but it presents the same difficulty for determination, and I am unable to assign 

 it to any species ; these various casts do not show whether the inner margins were 

 furnished with crenulations. 



4. Nucula cardioides, Edwards, MS. Tab. XIX, fig. 8. 



A single specimen from Pegwell Bay, in the cabinet of Mr. Edwards, has the above 

 name attached to it, and it appears to belong to a distinct species ; but it is very imper- 

 fectly preserved, and I am unable to describe its true characters. The shell is externally 

 rayed with distinct and well-marked striae or riblets, and the inner margin is crenulated. 

 Its present name must be considered provisional. 



5. Nucula compressa, J. Soicerby. Tab. XIX, fig. 5. 



Nucula compressa. J. Sow. Geol. Trana., vol. v, 2nd ser., p. 136, pi. 8, fig. 14, 1834. 



— — Prestwich. Geol. Journ., 1847, p. 405. 



— — Morris. Catal. Brit. Foss., p. 217, 1854. 



