40 BULLETIN OF THE 



EXPLANATION OF PLATES. 



PLATE I. 



Fig. 1. Obolella crassa, hc.il, var. ; a, dorsal valve ; b, interior cast of the same, 

 the features of the central area exaggerated to explain theoretical views ; c, the 

 same, in its normal state ; d, the interior surface of the dorsal valve diagrammati- 

 cally represented ; e, the interior cast of the ventral valve ; /, the interior surface 

 of the ventral valve diagrammatically represented. 



In the diagrammatic figures: x, cardinal area; a, cardinal muscles; <I, lateral 

 muscular scars ; c, central muscular scars ; p, a notch in the cardinal area. 



Fig. 2. Obolella ; a, ventral valve ; b, interior surface of the same ; c, a diagram- 

 matic representation of the same. 



Fig. 3. Prol)ahly a cast of an operculum of some species of HyoUthes. 



Fig. 4. FordiUa Troyensis, Barrande ? 



Fig. 5. Lamellibranch ? 



Fig. 6. Scenella reticulata, Billings ; a, lateral view ; b, outline of base. 



Fig. 7. Stenotheca rugosa, var. pauper. 



Fig. 8. Stenotheca curvirostra, sp. n. 



Fig. 9. Stenotheca rugosa, var. abrupta ; a, normal type ; b, a single larger speci- 

 men. 



Fig. 10. Platyceras primcevum, Billings ; a, seen from above ; 6, an umbilical view 

 of the same, specimen laterally compressed. 



PLATE II. 



Fig. 10. Platyceras primcevum, Billings ; c, a specimen of normal type. 



Fig. 11. Pleurotomaria (Raphistoma) Attleborensis, sp. n. 



Fig. 12. Paradoxides Walcotti, sp. n. 



Fig. 13. Miscrodiscus lobatus, Hall. 



Fig. 14. Ptychoparia Attleborensis, sp. n. 



Fig. 15. HyoUthes quadricosfatus, sp. n. Ventral view ; a section near its larger 

 extremity, and a basal view of the septum. 



Fig. 16. HyoUthes Americanus, Billings ; ventral view, and cross-section near its 

 larger extremity. 



Fig. 17. HyoUthes communis, var. Emmonsi, Ford ; dorsal view, with cross-section 

 of its larger extremity, and basal view of the septum. 



Fig. 18. Aristozoe? 



Fig. 19. Microdiscus belli-marginatus, sp. n. ; a, head ; b, pygidium. 



