PLATE X. 



Fig. 



18. Streptorhynchus pelargonatus, ScUotheim. Testiferous specimen (large valve), 



twice the natural size. Dalton-le-Dale. 



19. — — Another specimen, differing in form. Dalton-le-Dale. 



20. — — Another variety. Dalton-le-Dale. 



21. — — Lateral view (twice the natural size) of a cast. Dalton-le- 



Dale. 



22. — — Cardinal view of the last, showing the area and deltidium. 



23. — — 



24. — — 



25. — — 



26. — — ] Cardinal view (twice the natural size) of other specimens : 



27. — — J «3 the deltidium or closed fissure. Dalton-le-Dale. 



28. — — Enlarged view of the posterior half of the shell, showing 



the dental plates {a) and socket-plates {b). Tunstall 

 Hill. 



29. Productus horridus, /. de C. Sowerhy. Front view (natural size) of the large valve 



of a testiferous specimen. Garmundsway. 



30. — — Umbonal view of the last specimen. 



31. — — Lateral view of the same. 



Testiferous specimens, twice the natural size, looking on 

 the small valve and area {a). Dalton-le-Dale. 



