PLATE LXI. 
(Figures l-'O, ‘ill, 2 ;?, ‘27, 28, 32, 37, 38 by G. B. SIMPSON ; II, l‘2”l)y l{. P. WHITFIELD ; 13-19, 21, 2/, ‘25, 26, 29-31, 33-35 by 
F 15. Meek ; 21,36 by E. Emmons.) 
Genus CYCLORHINA, gen. nov. 
Pane -iiiii. 
Cycloriiina nobilis, Hull. 
Fig-s. 1, 2, 4, 5. Ventral, protiLe, dorsal and cardinal views of a young- shell; showing the obtuse umbones, 
deeply truncated beak of the pedicle-valve, straight cardinal line, and low median fold and 
sinus. 
Fig. 3. The interior of the umbonal portion of the brachial valve; showing the divided hinge-plate and 
its thickened lateral divisions. X 3. 
Figs. 6-9. Profile, cardinal, frontal and ventral views of a mature individual. 
Fig. 10 An enlargement of the external surface ; showing the fine concentric lines' which crenulate upon 
the crest of each plication. X 3. 
Hamilton group. Thedford, Ontario. 
Fig. 11. The interior of an incomplete pedicle-valve; showing the teeth, and the scars of the pedicle, 
adductor and diductor muscles. 
Fig. 12. A weathered specimen ; showing the cavities occupied by the crura. 
Hamilton group. Darien, N. T. 
Genus RATONIA. Hall. 
Pago 201. 
EaToNIA SINGUL.tUIS. VjUULKCm. 
Fig. 13. Ventral view of an unusually lai’ge specimen. 
Figs. 14-16. Cardinal, frontal and profile views of a normal example. 
Lower Helderberg group (Shaly limestone). Albany county, iV. Y. 
Eatonia peculiauis. Conrad. 
Fig. 17. Dorsal view of an average specimen. 
Lower Helderberg group (Shaly limestone). Albany county, N. Y. 
Fig-. 18. The interior of a brachial valve, viewed in profile from the front; showing the elevation of the 
cardinal process, its lobation and the crura. 
Fig. 19. An internal cast of the pedicle valve ; showing the impressions of the adductor and diductor 
musculai- scars and pallial sinuses. X 2. 
Oriskany sandstone. Albany county, N. Y. 
Fig. 20. The interior umbonal portion of the brachial valve, enlarged ; showing the elongated lobes of the 
cardinal process, each of which bears a median groove ; the divergent crural apophyses are 
attached to the body of the process beneath these lobes. X 3. 
Oriskany sandstone. Cumberland, Maryland. 
Fig. 21. An internal cast of a brachial valve; showing the impression of the hinge-plate and muscular 
scars. 
Oriskany sandstone. Albany county, iV. Y. 
Fig. 22. Fi-ont marginal view of a specimen ; showing the development of median fold and sinus and the 
dentate margins. 
Lowei- Heldei-berg group (8haly limestone). The Helderbergs, N. Y. 
Figs. 23, 24. The interior of brachial valves ; showing the variation in form of the cardinal process. Fig¬ 
ure 24 represents an old shell in which the process and socket-walls have become thickened 
and the parts consolidated. 
Fig. 25. The interior of a pedicle-valve; showing the open delthyrium, marginal teeth, large diductor 
scars, small adductors with strongly elevated posterior walls; the dentate shell margins and 
Ungulate extension of the median sinus. 
Oriskany sandstone. Cumberland, Maryland. 
Fig. 26. An internal cast of the pedicle-valve. 
Oriskany sandstone. Albany county, N. Y. 
