29 



the common recent species Valvata piscinalis of Lam. Upon examining 

 my specimens of this latter shell, I find among them two distinct 

 varieties or perhaps species. It is remarkable that Fleming in his specific 

 character of this shell says *' pillar with a large central cavity " 

 [or umbilicus) and a few lines after, in the description, he says, 

 "central cavity distinct^ but not large:" but it is also remarkable that 

 one principal difference between the two varieties or species (as the case 

 may be) which I possess, consists in this very circumstance ; it is there- 

 fore probable thar this apparent discrepancy may be reconciled by the 

 supposition that when drawing out his specific character Fleming had in 

 view a specimen with a large umbilicus, and afterwards when giving a 

 more detailed description he accidentally observed one with a small 

 umbilicus. 1 am much disposed to regard these two recent sorts as 

 distinct species, but I should prefer leaving it undecided until an oppo- 

 tunity occurs of examining more specimens from other localities. But 

 I must compare the fossil with both the recent sorts. First, let me 

 examine comparatively the dimensions of the three ; the fossil one 

 (No. 1) is much larger than either of the recent ones, and of these 

 latter, that with the large umbilicus, (No. 2.) is much larger than 

 that virith the small umbilicus (No, 3.). Next, let me examine com - 

 comparativel} the /)ro/)or<zons of the three sorts; No. 1, iu its greatest 

 length measures 34 hundredths of an inch, and in its greatest breadth 

 26 hundredths ; the length and breadth of No. 2, are exactly equal ; and 

 No. 3, is rather wider than it is long ; the proportions of the three sorts 

 differ therefore very evidently. Further, as regards other characters ; 

 the sutures in No. 1 , and No. 2, are equally distinct and deep, while 

 that of No. 3, is not nearly so strongly marked : the volutions in No. 2, 

 are regularly rounded, while those of No. 1, increase gradually from 

 the upper toward the lower parts, though they are still very nearly regu- 

 larly rounded, while in No. 3, they increase still more gradually. In 

 No. 1, there are six volutions, in No. 2, there are five, and in No. 3, 

 scarcely four and an half. 



