EXPLANATION OF THE PLATES AND WOOD-CUTS. 



species. We possess fragments which retain this structure, but are not sure they 

 belong to the present species. 

 Loc. Petherwin, Barnstaple. 

 Fig. 3. Leptfsna Fragaria, var. If this fossil be referrible to the species described in 

 PI. LVI. figs. .5, 6, it is a very strongly-marked variety ; but we are not satisfied 

 that it is a distinct species, although the tubercles are more elongated — allowance 

 must be made for the state of preservation. 

 Loc. Petherwin (abundant). 

 Fig. 4, Atrypa Mspida. Transversely oval, compressed, furnished with concentric 

 fringes of spines. 

 Loc. Petherwin. 

 Fig. 5. Atrypa decussata. Subglobose, slightly compressed ; front even, straight ; 

 surface concentrically striated and decussated ; beak of the lower valve very little 

 prominent, with a trifling angle on each side. 

 Loc. Petherwin. 

 Fig. 6. Atrypa indentata. Transverse, obovate, with an indented front ; the edge of 

 the lower valve elevated ; its beak small, prominent. 



The front of this shell appears as if impressed by the finger, whence its name : 

 the elevation in the margin of the lower valve does not affect the surface of the 

 other ; this may serve to distinguish it from A. ohovata (Silur. Syst. PI. VIII. fig. 

 9), to which it bears a very close affinity. 



Loc. Petherwin (with the last, abundant), Barnstaple. 

 Fig. 7. Atrypa suhdentata. Oi'bicular, slightly convex, rather longer than wide, with 

 a pointed three-plaited raised front ; beak minute. 

 Loc. Petherwin. 

 Fig. 8. Atrypa Unguiculus. Hemispherical, rather wider than long, with an inflated 

 beak, smooth ; front emarginate ; lower valve very convex, its beak channelled ; 

 upper flat, with a central impressed line. 



This pretty shell occurs abundantly in the Petherwin strata, and is very cha- 

 racteristic of them ; it is frequently twice the size of the specimen figured. 

 Loc. Petherwin, Barnstaple. 

 Fig. 9. Atrypa triangularis. Triangular, with two folds in the front, beak scarcely 

 prominent. 



Very much crushed and distorted casts in soft ferruginous stone. 

 Loc. Petherwin. 

 Fig. 10. Atrypa striatula. Suborbicular, convex, finely striated. A large species. 



Loc. Petherwin, Barnstaple, Fowey ? 

 Fig. \\. Spirifera extensa. Fusiform, convex, radiated ; about 7 ribs 'are elevated 

 in the middle of the upper valve ; its beak small ; radii numerous, commencing 

 along the hinge-line. 



Loc. Barnstaple, Barnstaple Bridge, Saunton, Petherwin. 

 Figs. 12, 13. Spirifera disjuncta. Semicircular, with an emarginate front, very con- 

 vex, radiated ; upper valve with about 12 ribs, much raised in the front, forming 



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