PLATE LVlll. 



(Figures 1-10, 15-ia, .i4, 35, 36, 40 by G B. Simpson; 11, 12, 14, 35 by E. ESISIONS; 13, 20- J3, 26-33 by F. b. MEEK.) 



GENU.S KHYNCHOPORA, King 



Page 210. 



Rhynchopoka pustulosa, Wliile. 

 Pigs. 1-4. Dorsal, ventral, front and profile views of an aveiage example. 

 Burlington limestone. BnrlingUm, Iowa. 



(Jenus WILSONIA, (Quenstedt) Kaysek. 



Page 195 

 WiLSONIA Saffokdi, Hull. 

 Pigs. 5-7, 10. Dorsal, ventral, frontal and profile views of a normal adult individual. 

 Figs. 8, 9. Pront and profile view.-* of another specimen, with broader median fold and greater anterioi' 



gibbosity. 

 Fig. 11. The interior of a pedicle-valve ; showing the teeth and muscular impressions. X 2. 

 Fig. 12. Cardinal view of an internal cast of conjoined valves; showing the muscular impressions and the 



cavities left by the dental plates and median septum. X 2. 

 Niagara group. Perry county, Tennessee. 



WiLSONIA \entkicosa, Hall. 

 Fig. 13. Profile view of an average specimen ; showing the extreme gibbosity of the valves. 

 Kig. 14. The interior of a thickened pedicle-valve ; showing the scars of the pedicle and diductor muscles. 

 Lower Helderberg group (Upper Pentamerus limestone). Schoharie county, N. Y. 



Genus UNCLNULUS, B.^yle. 



Page 195. 



Uncinulus abruptus, Hall. 



Fig. 15. The interior of the urabonal portion of the pedicle-valve ; showing the marginal teeth with dental 

 plates lying close against the shell-walls. X 2. 



Fig. 16. Cardinal view of the articulating apparatus of the brachial valve of a young shell ; showing the 

 triangular, divided cardinal process and the elevation of the crura. X 3. 



Figs. 17, 18. Two views of the corresponding parts in an adult shell in which the lobes of the cardinal prin- 

 cess and the lateral poi-tions of the hinge-plate are considerably thi<:kened. X 2. 



Fig. 19. The interior of a pedicle-valve ; showing the faintly defined muscular scar. 



Figs. 20, 21. Dorsal and front views of conjoined valves of a typical specimen. 



Lower Helderberg group (Shaly limestone). Albany and Schoharie counties, N. Y. 



Uncinulus muxabilis, Hall. 



Figs. 22, 2.^. Profile and front views of a mature shell ; showing its subspherical shape. 

 Figs. 24, 25. Two views of the intei-ior umbonal region of the brachial valve ; showing the thickened 

 median septum, curved and elevated crura and bilobed cardinal process. X l-J. 



Lower Helderberg group (Shaly limestone). Albany and Schoharie counties, N. Y. 



Uncinulus nobilis. Hall. 



Fig. 26. Pront marginal view of an adult shell. 



Lower Helderberg group (Upper Pentamerus limestone.) Albany and Schoharie 



counties, iV. Y. 



Uncinulus pykamidatus, Hall. 



Figs. 27, 28. Profile and front views of an average specimen. 



Lower Helderberg group (Shaly limestone). Albany county, N. Y. 



