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PLATE LXI 



.--..» .-«. ., .. .. ., 3. 3. 3S ., V-':;— ^1\ f-^'/- WH....... . .-,«, .. ., ., ., .,,. 33^ ., 



I 15. .tlELK , Jl,.i6 by E. Kmmons.) 



Genu.s CYCLORHINA, gen. nov. 



Pai^e -.'hi;. 



Cyclorhina nobilis. Hull. 



deeply t,uncated beak of the pe.i.cle-valve, straight cardinal line, and low median fold and 



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F.^. 6-9 ProHle, cardinal, frontal and ventral views of a mature individual. 



f If?- 10 An enlargement of the external surface ; showing the fine concentric lines which crenulate upon 

 the crest of each plication. X 3. 



Hamilton group. Ttiedford, Oiitarm. 

 Fig. 11. The interior of an incomplete pedicle-valve; .showing the teeth, and the scare of the pedicle, 



adductor and diductor muscles. 

 Fig. 12. A weathered specimen j showing the cavitie.<! occupie<l Iiy the crura. 

 Hamilton gi-oiip. Darien, N. ¥. 



Genus K ATOM A. Hall. 



Pll^U J()«. 



Eati>nia sinoui.aki.s. Viiiiii.voin. 



Figr. 13. Ventral view of an unusually lai-ge specimen. 



Figs. 14-16. Cardinal, frontal and profile views of a normal exam]>le. 



Luwer Helderberg gmuyi (Shaly limestone). Albany county, N. Y. 



Eatonia peculiauis. Conrad. 



Fig. 17. Doi-sal 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 pro<'ess, its lobation and the crura. 

 Fig. 19. An internal cast of the pedicle valve ; showing the impressions of the adductor and diductoi- 



muscular scai-s and pallial sinuses. X 2. 



Oriskany sandstone. Albany cownty, N. Y. 

 Fig. 20. The interior uinbonal 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. CumberlaHd, Maryland. 

 Fig. 21. An internal cast of a brachial valve; showing the impression of the hinge-plate and muscular 



scai-s. 



Oriskany sandstone. Albany county, N. Y. 

 Fig. 22. Front marginal view of a specimen ; showing the development of median fold and sinus and the 

 dentate margins. 



Lower Helderberg group (Shaly 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 

 scai-s, small adductors with strongly elevated posterior walls; the dentate shell margins and 

 Ungulate extension of the me<lian sinus. 



Ori.skany sandstone. Cumberland, Maryland. 

 Fig. 26. An internal cast of the pedicle-valve. 



Oriskany sandstone. Albany county, N. Y, 



