PLATE LXI. 



IFiguivs I'd. -.M, a'i, ■>?, M, 3-J, 37, :js l)y G. li. SiMi'SON ; 11, |-2"l)y U. P. Whitkiei.T) ; I:i-1H, 'Jl, 'iJ, 25, 20, 29-31, 33-35 by 



F B. Mekk ; 21,:i(; by E. Kmmdns.) 



Genu.s CYCLORIIINA, gen. nov. 



Cyclokhina NOBILIS, Hull. 



Fig's. 1. 2, 4, ."). Ventral, protile, dorsal ami cardinal views of a youngs shell; showing the obtuse umbones, 



deeply truncated beak of the iiedichwalve, straight cardinal line, and low median fold and 



sinus. 

 Fig. 3. The interior of the umbonal jiortinn of the bi'arhial valve ; showing' the divided hinge-plate and 



its thickened latei'al divisions. X ^• 

 Figs. 6-9. Pi'otile, ('.irdinal, frontal and ventral \iews of a mature individual. 

 Fig. 10 An enlargement of the external surface ; .showing the tine concentric lines which crenulate upon 



the crest of each plication. X K. 



Hamilton group. Thedfvrd, (hifaria. 

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



adductor and diductiu' muscles. 

 Fig. 12. A weathered specimen ; showing the cavities occupied by the ci-iira. 

 H;imiIton gi-oup. Darien, N. 1". 



Genus EATONIA. Hall. 



Fide Jul. 



K.vTi-NL\ f;iN(!UL.\i;is. V;iini.\(iii. 



Fig. 13. Ventral view of an unu.sually large specimen. 



Figs. 14-lli. Cai'dinal, frontal and prcjtile views of a normal example. 



Lower Helderberg group (Shaly limestone). Alhani/ coiiiily, N. Y. 



Eatonia PECULiAUi.s. (_'i)nrad. 



Fig. 17. Dorsal view of an average speinmen. 



Lower Helderberg gi-oup (Shaly limestone). Albany county, N. Y. 

 Fig'. IS. The interior of a brachial valve, viewed in i)rotile from the front ; showing the elevation of the 



cardinal process, its lobation and the crura. 

 Fig. 19. An internal cast of the i)e<licle valve ; showing the impressions of the adductor and diductor 



muscular scars and pallial sinuses. X 2. 



Oriskany sandstone. Albany coimty, 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 pruce-ss 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 



scai's. 



Oriskany sandstone. Albany county, N. Y. 

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

 dentate margins. 



Lower Heldei-bei-g group (Shaly limestone). The Hcldtrbergs, N. Y. 

 Figs. 23, 24. The interior of brachial valves ; showing the variation in form of the cardinal pi-ocess. Fig- 

 ure 24 represents an old shell in wliicli 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 po.sterior walls ; the dentate shell margins and 

 Ungulate exten.sion of the median sinus. 



Oriskany sandstone. Ctimherlaiid,, Maryland. 

 Fig. 26. An intei-nal cast of the jjedicle-valve. 



Oriskany sandstone. Albany county, N. Y, 



