610 Contributions to Invertebi^ate Paleeontology. 



EXPLANATION OF THE PLATES. 



PLATE V. 



Streptokhynchps hydraulicum Whitf. Page 508. 

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

 Figs. 2 and 3. Views of a dorsal valve, natural size and enlarged. 



Spirifera Vanuxemi Hall. Page 509. 

 Fig. 4. View of a very large dorsal valve. 

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



Meristella l;evis Vanuxem. Page 510. 



Fig. G. Cast of a ventral valve. 



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



Meristella bella Hall. Page 510. 



Fig. 8. View of a ventral valve. 



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

 of the internal spires. 



NncLEOspiRA rotundata Whitf. Page 511. 



Figs. 11 and 12. Casts of ventral valves. 



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

 rotund specimen. 



Retzia FORMOSA Hall. Page 512. 



Fig. 15. View of a small dorsal valve. 



Fig. 16. View of- a ventral valve enlarged. This individual resembles the 

 form common in Tennessee. 



Rhynchonella hydraulica Whitf. Page 512. 



Fig. 17. View of a cast of a dorsal showing the form of the shell as noticed in 

 several specimens. 



Pentamerds pes-ovis Whitf. Page 513. 



Figs. 18-21. Views of casts of ventral valves, showing some variations in form. 

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



Pterinea aviculoidea Hall. Page 514. 

 Fig. 23. View of a left valve showing the general form. 



