FOSSIL SHELLS OF THE CRAG. 233 



Pectunculus pilosus, Auct. PI. xiii. fig. 7. 



Pectunculus glycimeris, Turton. Pectunculus polyodonta, Goldf. 



„ pulvinatm, Brongn. „ variabilis, Min. Con. 



„ obovatusj Lam. 



Red crag, passim. Coralline crag, Ramsholt and Sud- 

 boume. 



An abundant shell in both the red and coralline deposits, 

 and very variable. I have included the whole of the above 

 synonymes, considering them all to refer to the same species. 

 Among a hundred specimens of the crag fossil, some may be 

 found thick, tumid, and longitudinal ; others thin, lenticular, 

 and transverse. After a careful examination of an immense 

 series of specimens, I cannot detect any character sufficiently 

 permanent to vrarrant a separation of the crag fi-om the re- 

 cent shell. The number of teeth in the younger shells is up- 

 vrards of twenty, but the central ones become obhterated. 

 The large obtuse angle on one side is rather more strongly 

 marked in the recent shell, but it is visible in most of my 

 specimens. At most it would only constitute a variety. One 

 antiquated specimen in my possession has only three teeth 

 remaining. The chevron-formed lines in the ligamental area 

 (from five to eight), are deeply impressed in some specimens 

 but obsolete in others, even when the valves are found united, 

 so that the above condition could not be a result of subsequent 

 attrition. My largest specimen measures a little more than 

 three inches across, but a magnificent specimen of the recent 

 shell from the Mediterranean, in the possession of Mr. G. B. 

 Sowerby, has attained the diameter of nearly six inches. 



A number of specimens of the same species from Sicily, 

 obligingly sent me by Madame Power, exhibit the same va- 

 riations in character, although a slight obliquity prevails 

 among the generality of them. 



I have given a figiu-e of this shell, for the purpose of show- 

 ing the difference between it and another crag Pectunculus^ 

 which I regard as new. In many instances however the for- 

 mer shell contrasts much less strongly with the new species, 

 than in the one which I have had drawn for illustration. 



Pectunculus suhobliquus, Nob. PI. xiii. fig. 6. 



iticular, sub -inequilateral, s 

 ransverse lines of growth, m; 



Red crag, Walton-Naze. 



Shell lenticular, sub -inequilateral, slightly oblique, longitudinally striated 

 with transverse lines of growth, margin crenulated. Diameter 2 inches. 



