PLATE LXI— Continued. 



Eatonia Whitfieldi, Hull. 



Figs. 27, 28. Ventral and dorsal views of a rather small shell ; showing the plicated exterior. 

 Oriskany sandstone. f'winherJand, Maryland. 



EaTONIA MEDIAI/IS, VailllXclll. 



Figs. 29, 30. Dorsal and profile views of an average example j 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 lunbonal cavity of a specimen in which a small portion of the lirachial 

 valve is in articulation with the pedicle-valve; showing the stout cardinal process with the 

 crura arising from its base, and the adductor muscular scars with their elevated posterioi- 

 wall. 



Fig. 33. An internal cast of an old jiedicle-valve with unusually large muscular seal's. 



Fig. 34. Ventral view of the specimen repi'esented in figures 29, 30. 



Fig. 3.5. An internal cast of an average I'edicle-valve. 



Lower Helderberg group. Albany and iSclioliarie i-imntles, N. Y. 



Eatonia sinuata. Hull. 



Fig. 36. A brachial valve of average size from which the shell is partially exfoliated, exposing the cast of 



the cardinal process and showing the adductor scars. 

 Fig. 37. An enlargement of the cardinal process viewed fi-om in fi-ont ; showing the short crural bases 



below, and the stout lobes above. X 3. 

 Fig. 38. An internal cast of the brachial valve ; showing the four scars of the adductor muscles. 



Lower Helderbei-g group (originally cited as Oriskany sandstone). Cumberland, Md. 



