1 
PLATE LXI—Continued. 
Eatonia Whitfiei.di, Hall. 
Fig'S. 27, 28. Ventral and dorsal views of a rather small shell; showing the j)licated exterior. 
Oi'iskany sandstone. Cumberland, Maryland. 
Eatonia MEDiALis, Vaiiuxcni. 
Figs. 29, 30. Dorsal and pi'otile views of an average example ; showing the exterior characters. 
Fig. 31. Front view of a large .shell; showing the development of the median fold and sinus. 
Fig. 32. An oblique view into the umbonal cavity of a specimen in which a small portion of the brachial 
\'alve is in articulation with the pedicle-valve; showing the stout cardinal process with the 
crura ai'ising from its base, and the adiluctoi' musculai' scai's with their elevated posterior 
wall. 
Fig. 33. An intei'nal cast of an old j^edicle-valve with unusually large muscular scai-s. 
Fig. 34. Ventral view of the specimen I'ei^j'esented in tigures 29, 30. 
Fig. 35. An internal cast of an average pedicle-valve. 
Lower Helderbei'g group. Albany and /Slchol/arie cotmtics, fV. Y. 
Eaton IA sin data. Hall. 
A brachial valve of average size from which the shell is pai-tially exfoliated, exposing the cast of 
the cardinal process and showing the adductoi' scars. 
An enlargement of the cardinal process viewed fi'om in front ; showing the short crural bases 
below, and the stout lobes above. X 3. 
An internal cast of the brachial valve; showing the foui' scars of the adductor muscles. 
Lower Helderberg grou}") (originally cited as Oriskany sandstone). Cumberland, Md. 
Fig. 36. 
Fig. 37. 
Fig. 38. 
