PLATE LXI— Continued. 



Katonia Whitfiei.di, Hiill. 



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

 Oriskany sandstone. Cumberland, Maryland. 



Eatonfa mediams, Viiiiiixoni. 



Figs. 29, 80. Uorsal and profile views of an average example ; showing the exterior characters. 



Vig. 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 

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

 crura arising from its base, and the adductor muscular scmrs with theii- elevated jjosterior 

 wall. 



Fig. 33. An internal cast of an old i>eilicle-valve \vith imusually large muscular scans. 



Fig. 34. Ventral view of the specimen represented in figures 29, 30. 



Fig. 85. An internal cast of an average pedicle-valve. 



lyower Helderberg group. AVtany and JSclwhar'w oountics, N. Y. 



Eatonia sinuata, Hull. 



Fig. 36. A bi-achial valve of average size from which the shell is j)artially exfoliated, exposing the cast of 



the cardinal process and showing the adductor scars. 

 Fig. 37. An enlargement of the cardinal process viewed from in front ; 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 scare of the adductor muscles. 



Lower Helderberg gi-oup (originally cited as Oriskany sandstone). Cumberland, Md. 



