EXPLANATION OF THE PLATES AND WOOD-CUTS. 



Fig. 24. Atrypa cuhoides. Subglobose, striated ; front raised, very flat, with a deep 

 square sinus in the margin, edges sharp, projecting ; stri« numerous, shallow, 

 about 15 are elevated; beak small, acute; lower valve small, nearly flat, with a 

 large projecting square appendage filling the sinus in the upper one ; striae nume- 

 rous, shallow, extending to the beaks, those on the side much curved. 



The parallel striag on the front are a striking character. 



Loc. Plymouth, also in the Eifel. 

 Fig. 25. Atrypa latissima. Transversely elongated, smooth, convex, with rather 

 pointed dependent sides ; front elevated, broad, rounded and furrowed, furrows 

 shallow, many very obscure on the sides. 



Nearly related to A. platyloba (M. C. t. 496, f. 5, 6.), but the front is rounder, 

 and the furrows much less distinct. 



Loc. Plymouth. 



Plate LVIL 



Fig. 1. Atrypa squamosa. Lenticular, ribbed, squamose. 



The ribs are thick, sometimes forked, and are crossed by concentric thin la- 

 minae ; they vary in number, and are sometimes so numerous that it is difficult to 

 draw a line of demarcation between this species and T. aspera of Schlotheim, 

 which again passes into A. affinis (Silur. Syst. PI. VL f. 5. M. C. t. 324.). 

 Loc. Plymouth. 



This shell appears to characterize a stratum of limestone in the Eifel. 

 Fig. 2. Atrypa impleta. Transversely elongated, ventricose, furrowed ; sides rounded ; 

 front elevated with six furrows ; beaks slightly prominent, much wider than long. 

 The furrows on the surface are shallow and extend to the beaks, the ribs be- 

 tween them are rounded. 

 Loc. Plymouth. 

 Fig. 3. Atryjja sphcerica. Spherical or rather obovate, transverse, ventricose, plaited; 

 edge of the front deeply sinuated, with five elevated ribs ; beak small, adpressed. 

 Rather wider than long. 

 Loc. Plymouth. 

 Fig. 4. Atrypa implexa. Obovate, transverse, plaited. Front straight, flat; margin 

 of the front and sides broad ; the toothed edges of the valves deeply locked into 

 each other ; plaits numerous, acute. 



At first sight this may be taken for Atrypa Wilsoni (M. C), but it is not so cy- 

 lindrical, neither is the front so deeply sinuated. 

 Loc. Plymouth and the Eifel. 

 Figs. 5 and 6. Atrypa primipilaris , Schloth. (Von Buch. Terebr. 68, T. II. p. 29. 

 Spirifer pentagonus, Sower. See Encyc. Metrop. loc. cit.) Pentagonal, convex, 

 plaited ; front elevated, with three or more plaits, margin flattened ; a deep angu- 

 lar furrow runs along the middle of the lower valve, bounded by two angular 

 ridges ; beak prominent. Fig. 6 represents a young shell. 

 Loc. Plymouth, Eifel. 

 Fig. 7. Spirifera (?) crenistria, Phill. (Geol. of Yorksh., 216, PI. IX. f. 6. Sp. reticu- 



