220 ORGANIC REMAINS. 



striking, sometimes barely perceptible, they can scarcely be viewed 

 as the characters of a distinct species. The specimen figured, which 

 is from the front of Coldmoor, retains something of its original purple 

 colour. 



Fig 11 (PI, VII) represents a shell of a similar form from the 

 oolite. The depression at the truncated end is rather deeper than in 

 No. 8, and the other end is broader and more rounded. Besides, 

 the shell is not only striated, but antiquated ; a character which is 

 seen very faintly, if at all, in No. 8, and other specimens of this 

 donax from the aluminous strata. This fossil is sometimes met with 

 of a considerable size, measuring above three inches in its greatest 

 diameter. 



We are at a loss to decide, under what genus the shell figured 

 in PI. VII. No. 12, should be placed ; but it seems to be related to 

 the donax family. Mr. Parkinson, who is equally at a loss to class 

 it, has figured it in his Organic Remains, III. PI. XIII. Fig. 16. Our 

 specimen, like his, is a cast; but is much more perfect and beautiful. 

 We have other specimens with the shell, but less perfect. The shell 

 is marked with the same kind of straight ribs, passing across each 

 valve in a peculiar form ; those from the anterior slope being nearly 

 at right angles with the line of that slope, and those from the 

 posterior slope leaving it also at right angles ; so that, as the two 

 slopes make an obtuse angle at the beak, the two sets of ribs on each 

 valve, those at least that are not remote from the beak, converge in 

 the middle of the valve, in a line passing from the beak to the base. 

 Towards the beaks, there are a few slight cross markings, between 

 the two sets of ribs. In the shell, at least in the larger and ( we 

 may presume) older specimens, the ribs do not reach the margin; 

 but each valve has a plain border, beyond the ribbed part, marked 

 only with concentric striae. A few concentric or transverse lines also 

 cross the ribbed part of the shell. This curious fossil shell occurs 



