234 ORGANIC REMAINS. 



ribs, with transverse membranaceous striae. It belongs to the 

 oolite, and the grey limestone. A shell resembling this and No. 3, 

 but with sixteen smooth ribs, occurs in the ironstone. 



Fig. 10 represents the inside of a handsome shell, of a larger size, 

 and more oblong shape, from the hard sandstone at the foot of Scarbo- 

 rough castle. Some specimens are three inches long, but it is very 

 difficult to get any entire. Both valves are convex, and, as in No. 12, 

 are closely invested with transverse membranaceous striae, somewhat 

 sharp and rough, crossing both the ribs and the intermediate grooves. 

 There are nine ribs, which are broad and rather flat, but each has an 

 elevated ridge running along the middle of it, surmounted here and 

 there with oblong spines, or sharp scales, crossing the ridge. As this 

 species does not appear to have been hitherto described, we may 

 name it p. Scarburgensis. 



No. 11 agrees pretty well with p. pusio; but one of the ears in 

 our fossil has no distinct line of separation between it and the valve.^ 

 The specimens, which are all from the oolite, differ considerably ; 

 their numerous filiform ribs being more or less crossed by transverse 

 scaly wrinkles. In some, the ribs are minutely echinated, and alter- 

 nately smaller ; and as the number of the ribs is seemingly doubled 

 where this alternation takes place, such specimens are allied to 

 2^. islandicus or cinnabarinus. 



No. 1 is a beautiful shell from the Malton oolite, which we have 

 not seen described by any author. It is nearly circular, and is 

 commonly about two inches in diameter. The ears resemble those 

 of No. 9 ; and the valves, instead of being ribbed, are adorned with 

 innumerable longitudinal striae, finely waved, scarcely visible at the 

 beaks, but growing more and more distinct towards the margin. 

 These striae are crossed by a few concentric rings, which mark the 

 shell in the antiquated style, the margin growing lower and lower 

 beyond each successive ring. These rings have no determinate 



