PLATE I. 



PAGE. 



Figs. 1-3. Streptorhynchus hydrauucum Whitf 410 



1. View of a cast of a ventral valve, twice enlarged. 



2 and 'i. Views of a dorsal valve, natural size and enlarged. 



Figs. 4-5. Spirifera Vanuxemi Hall 411 



4. View of a very large dorsal valve. 



5. View of a ventral valve, also of large size. 



Figs. 6-7. Meristeeea e^Evis Vanuxem 411 



6. Cast of a ventral valve. 



7. View from a gutta-percha impression in the mould of a dorsal valve. 



Figs. 8-10. MERISTECLA BEEEA Hall 412 



8. View of a ventral valve. 



9 and 10. Opposite sides of an internal cast, the first showing indications of the in- 

 ternal spires. 



Figs. 11-14. NUCEEOSPIRA ROTUNDATA Whitf. 413 



11 and 12. Casts of ventral valves. 



13 and 14. Dorsal and profile views of an internal cast of a large and rotund specimen. 



Figs. 15-16. Retzia Formosa Hall 413 



15. View of a small dorsal valve. 



16. View of a ventral valve enlarged. This individual resembles the form common 



iu Tennessee. 



Fig. 17. Rhvnchonelea hydraueica Whitf 414 



17. View of a cast of a dorsal showing the form of the shell as noticed in several speci- 



mens. 



Figs. 18-22. Pentamerus pes-ovis Whitf. 414 



18-21. Views c feasts of ventral valves, showing some variations in form. 

 22. Cast of a dorsal valve showing the long and distant processes. 



Fig. 23. Pterinea avicueoidea Hall 415 



23 View of a left valve showing the general form. 



Figs. 24-26. Goniophora dubia Hall 415 



21. View of a right valve, natural size. 



25. Cardinal view of the two valves in outline. 



26. Enlargement of a similar valve. 



Fig. 27. LEPERDITIA aeta Conrad 417 



27. The right valve of a specimen enlarged showing slight indicatiousof the ocular 



tubercle. 



Figs. 28-30. LEPERDITIA ANGULIFERA Whitf. 418 



28 and 29. Views of a right and a left valve showing a very slight variation in form. 



30. Outline profile of the valves united. 



Figs. 31-32. Eurypterus Eriensis Whitf. 416 



31. View of a head-plate showing the rounded front, the small occular tubercles, and 



small single facets between them. 



32. View of the dorsal surface of the thorax lacking the terminal spine. 



