description of plates. PLATE I. [Notes respecting Plate I.—Fig. 4, which is referred to Orbicula is an outside cast in a very soft slate; it has been impossible to determine the texture of the shell. It resembles an Ancylus in shape and direction of the apex, but there are no certain marks by which I can determine whether the apex is directed forwards or backwards. It will probably prove to be a Ilelcion. Fig. 9.1 have allowed to stand as in the text a lingula, but the state of the valve at the umbo and the delicacy of the fossil, and the softness of the rock has raised a doubt in my mind respect" ing its perfection.] Fig. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 15. 16. 17. 18. 19. 20. 21. Cypricardia. Lateral view of the mouths of cells of an indeterminate species-. Diplograpsus. Orbicula excentrica. Diplograpsus dissimilaris. Nemagrapsus elegans. do capilaris. Microdiscus quadricostatus. Lingula ? Obolus ? Diplograpsus secalinus. Cladograpsus sp. indet. Diplograpsus foliosus. Cladograpsus dissimilaris. ' Atops trilineatus. Lingula striatus. Eliptocephalus asaphoides. Diplograpsus ciliatus. Glossograpsus setaceus. Staurograpsus dichotomous.