PLATE IX— Continued. 



Orthothetes defokmis, Hull. 



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



Lower Heliierberg- group. Borst's Mill, Schoharie county, N. T. 

 For illu.strations of other species of the genus, see Palfpontology of New York. Vol, II. plate xvii, 

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



Genus HIPPAEIONYX, Vandxem. 



Page 257. 



HipPARiONYX PROXiMus, Vaiuixeni. 



Fig. 33. The intenor of a brachial valve of a young individual ; showing the .strongly bifurcated process, 

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

 Oi-iskany sandstone. Cumberland, Maryland. 



Fig. 34. The cardinal proce.ss imd it.s adjoining parts, as obtained from a gutta-jiercha impression of a 

 natui'al cast of the interior ; natural size. This figure shows very cleai-ly the almost complete 

 ob.siilescence of the cardinal area, the marginal crenulations extending nearly to the base of the 

 process. 



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



diductor muscles. 

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

 projecting teetli. From a gutta-percha impression. 

 Oriskany sandstone. Albany coimty, jV. Y. 

 For other illustrations, see Palaeontology of New Yoik, Vol. III. plates Ixxxix ; xc ; xci, tigs. 4, 5 ; 

 and plate xvA of this volume. 



