PLATE IS— Continued. 



Oethothetes defokmis, Hall. 



Fig. 32. Front view of an individual retaining both valves. 



Lowei- Helderberg group. Borst's Mill, Schohat-ie county, If. T. 

 For illustration.s of other species of the genus, see Palfeontology of New York. Vol, II. plate xvii, 

 and ibid. Vol. IV, plates ix and x ; and this volume, plate xx, figs. 8, 9. 



Genus HIPPARIONYX, Vanuxem. 



Page 257. 



HipPARiONYX PROXiMus, Vaiuixeui. 



Fig. 33. The interior of a bi-achial valve of a young individual ; showing the strongly bifui-cated process, 

 high vertical ci'ural plates, short median septum, and faint muscular scars. 

 Oriskany sandstone. Cumberland, Maryland. 

 Fig. 34. The cardinal process and its adjoining parts, as obtained from a gutta-percha impression of a 

 natu7-al cast of the interior ; natural size. This figure shows very clearly the almost complete 

 obsolescence of the cardinal area, the marginal crenulations extending neai'ly to the base of the 

 process. 

 Fig. 35. A natural cast of the interior of a pedicle-valve ; showing the impressions of the adductor and 



diductor muscles. 

 Fig. 36. The extei'ior of the cardinal ai'ea of the pedicle-valve ; showing the covered delthyrium and the 

 projecting teeth. From a gutta-percha impression. 

 Oriskany sandstone. Albany county, 2V. Y. 

 For other illustrations, see Palseontology of New York, Vol. Ill, plates Ixxxix ; xc ; xci, figs. 4, 5 ; 

 and plate xvA of this volume. 



