PLATE 12. 



Puge 

 Figs. 1-5. StROPHODONTA DEMIS8A 81 



1, 2. Dorsal and Tentral views of a small individual. 



8-5. Dorsal and ventral views and profile of a larger specimen. This individual is the largest 

 one observed in the Corniferous limestone. 



Figs. 6-8. Strophodonta inequisteiata 93 



6, 7. Dorsal and ventral views of a specimen of ordinary size. 



8. Profile of a larger and very gibbous specimen. 



Figs. 9-11. Strophodonta patersoni. ? 89 



9. A ventral valve of a specimen of ordinary size, but more convex than usual. 



10. A profile of the preceding specimen. 



11. An enlargement of the strite from the same shell. 



Fig 12. Strophodonta inequiradiata 87 



12. The cast of a ventral valve which may belong to this species. 



Figs. 13-15. Strophodonta perplana ... 92 



13. A young individual corresponding in size and character to the original of S. crenittria 



as described in the Gceol. Report of the 4th District. 



14. A dorsal view of a large individual of the same species. 



16 A cast of the ventral valve of the same species in chert, from Indiana. 



Figs. 16-18. Strophomena rhomboidalis 76 



16. An individual with numerous regular undulations. This is of the type of S. undulata, of 



Vanuxem's Geol. Report of 3d District. 



17. A specimen with few strong undulations. 



18. A east of the ventral valve showing few undulations. 



