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SUPPLEMENT TO THE BRITISH 



" Shell small, orbicular, tapering to an elevated apex, giving the shell a somewhat 

 conical form ; margin smooth and rounded. Outer surface of valve smooth, with 

 numerous concentric lines of growth. The inner smooth and very concave. This shell 

 does not appear to have attained a larger size than is indicated in pi. ii, fig. 18 (Sup., PI. 

 X, fig. 9). It is from the fish-bed and the clays associated therewith in the Upper Lias 

 of Ilminster. By its form it is readily distinguished from any other species." 



I have been favoured with the loan of Mr. Moore's original examples, and it 

 appears to me that the figure published in the ' Geologist ' is not quite broad enough at 

 its anterior portion. The exterior surface of the shell is covered with fine, concentric, 

 raised striae. It is about one and a half lines in length and breadth. The five examples 

 lent me by Mr. Moore all agreed in shape and dimensions. 



13. Discina Davidsoni, Moore. Sup., PI. X, figs. 11, 11 a. 



Discina Davidsoni, Moore. Quart. Journ. of the Geol. Soc, vol. xxiii, p. 540, 



pi. xvi, fig. 29, 1867. 



All I know of this species (?) is contained in Mr. Moore's description : 

 " Shell small, rather elongate, ovate, conical ; vertex much elevated, almost central ; 

 anterior margin and sides rounded ; posterior margin rather truncated ; surface of the 

 shell covered by very fine concentric lines. In general form this shell is not unlike D. 

 Sandersii, Moore, from the Upper Lias Leptaena- and fish-beds, but the encircling stria? 

 are much finer. This species is widespread, and evidently not uncommon. It is usually 

 found attached to the interiors of dead shells. In this way I have found it in the body- 

 whorl of a large Cerithium nodalosum, Moore, from the Ammonites-Bucklandi beds of 

 Shepton Mallet, and also attached to the internal chambers of several Nautili, their casts 

 having been retained on the inner stony matrix. It occurs also in the metamorphosed 

 bed on shells at Windsor Hill. Another instance is in the phragmacone of a very large 

 Belemnite at Southerndown, where its concave side occupies the centre of the chamber, 

 giving it at first sight the appearance of the siphuncle of an Orthoceras. The only free 

 specimen, though not perfect, is from the Lower Lias of Bedminster Down." 



14. Discina Dundriensis, Moore. Sup., PI. X, figs. 13, 13 a. 



Discina Dundriensis, Moore. The Geologist, vol. iv, p. 98, pi. ii, fig. 15, 1861. 



Shell minute, conical, almost circular or a little broader than long ; apex subcentral ; 

 exterior showing numerous irregular concentric scale-like lines. 



