PLATE IX— Continued. 



Orthothetes defokmis, Hall. 



Kig-. 32. Fi-ont view of an indiviiiual I'etaiiiing both valves. 



Lower Heldei-berg- group. Borst's Mill, Schoharie caunty, N. Y. 

 For illusti-ations of other species of the genus, see Palfeontolog-y of New York, Vol, II. plate xvii, 

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



Genus HIPPARIONYX, Vanuxem. 



Page 257. 

 HiPPARIONYX PROXIMUS, VililUXeiU. 



FifT. 33. The interior of a l)i-achial valve of a young indivi<lual ; showing the strongly bifurcated process, 

 high vertical crural plates, short median septum, and faint muscular scars. 

 Oriskany sandstone. Cumberland, Maryland. 

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

 natural cast of the interior ; natural size. This iigui-e shows very clearly the almost complete 

 obsolescence of the cardinal area, the marginal crenidations extending nearly to the base of the 

 l>rocess. 

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



diductor musc'les. 

 Fig. 36. The exterior of the cardinal area of the pedicle-valve ; showing the covered delthyrium and the 

 projecting teeth. From a gutta-percha imj)ression. 

 Oriskany sandstone. Alba^iy county. N. Y. 

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

 and plale xvA of this volume. 



