EXPLANATION OF THE PLATES AND WOOD-CUTS. 



lata, Sowerby. See Encycl. Metrop,, loc. cit.) This shell is not very uncommon in 

 the mountain-limestone of the north of England and of Ireland ; it also occurs at 

 Matlock. The Irish specimens are often large, with deflected margins, which, with 

 other circumstances, induce us to believe this shell will prove to be a Leptcena. 

 Loc. Plymouth. 

 Fig. 8. Spirifera nuda. Semicircular, with prominent beaks, smooth, the middle ele- 

 vated, with a furrow on each side of it; edge obtuse. 

 Loc. Plymouth. 

 Fig. 9. Spirifera pulchella. Hemispherical, convex, smooth, with three large rounded 

 ribs ; edge sinuated ; beak of the lower valve large, incurved. 



This resembles Sp. crispa (Silur. Syst., PI. XII. f. 8.), but is smooth and has 

 fewer ribs. 



Loc. Plymouth. 

 Fig. 10. Spirifera subconica, var. (Anomites subconicus, Mart. Pet. Derb. PI. XLV. 

 f. G.) This is smaller and has a more curved beak than Martin's shell, but we 

 think it is the same species. 

 Loc. Plymouth. 

 Fig. IL Spirifera affinis. Lenticular, ribbed, ribs numerous, branched and crossed 

 by concentric thin laminae ; hinge-hne shorter than the width of the shell ; beak 

 of the lower valve prominent, with a triangular flat area. 



The prominent beak and large triangular area distinguish this from Atrypa as- 

 pera, Schloth. (Silur. Syst., PI. XII. f. 5.) which it much resembles ; it is a re- 

 markable shell. 

 Loc. Plymouth. 

 Fig. \2. Orthis tenuistriata. Semicircular, with the front straight, striated ; one valve 

 regularly convex, the other flatter ; hinge-area parallel, narrow. 



The fineness of the striae and the regular convexity, joined with the parallel 

 area, at once distinguish this and make us doubtful whether it be not a Lepteena ; 

 traces of spines are indistinctly visible. 

 Loc. Morebath. 

 Fig. li. Pileopsis vetusta (M. C. t. 607). The specimen figured is more involute and 

 even than the shell in Min. Conch., but examples pretty frequently occur much 

 more like that figure at Mount Wise, &c. 

 Loc. Plymouth. 

 Fig. 11'. Nerita deformis. Subhemispherical, obliquely flattened ; whorls rapidly in- 

 creasing, finely striated ; inner lip uneven, aperture ovate. 



This was formerly published (see Encyc. Metrop., loc. cit.) under the name of N. 

 spirata (M. C. t. 46o, f. 1,2.); but it is not so transverse or ventricose, and the 

 spire, though imperfect, could not have been so depressed. 

 Loc. Stonehouse Hill. 

 Fig. 15. Nerita speciosa. Conical, depressed, smooth?; whorls rapidly increasing, 

 the upper ones very convex, the lower rather square, with a central spiral depres- 

 sion above, concave beneath ; aperture subtrapezoidal ? Height and diameter 

 about equal, often 3 inches. 



3 



