PLATE LVI. 



(Figures 1-13, 16-2S, 28-34, 3ii,37, « by G. B. Simpson; 11, 15, H~-i7 by U. P. Whiti'Ield; 35, 38 by C. E. BEECHER; 



39-44 copies.) 



Genus RHYNCHONELLA, Fisciiek de Waldheim. 



Page 177. 



Rhynchonella loxia, Fi.-^cher tie Wtildlieiiii. 



Figs. 1-5. Dorsal, ventral, profile, frontal and cardinal views of a normal mature individual, retaining the 

 smooth external surface, and showing' the contour, acuminate median fold and sparse lateral 

 ]ilication. 

 Vtg. 6. Cardinal view of an internal cast ; showing the cavity of the dental plales and median sejitum. 

 This is the type of the genus Rhynchonella. 



Upper Jurassic. Ckaraschowa, Runsia. 



Genus PROTORHYNCHA, oen. nov. 



Page ISO. 

 Protokhyncha ^QUIRADIATA, Ililll. 

 Fig. 7. An internal cast of the brachial valve ; showing the length of the median .septum. X 2. 

 Fig. 8. The cardinal portion of the brachial valve, enlarged ; showing a clearly defined cardinal ,'irea, 

 oblique dental sockets, the broad, rather ill-defined hinge-plate, with a median cavity whose 

 lateral walls are continuous with the median septum. X 3. 

 Fig. 9. An internal cast of a larger i)edicle-valve ; showing a well defined median sinus and a very re- 

 stricted muscular scar in the umlional region. X 2. 

 Clinton group. New Hartford, N. T. 



Genus ORTHORHYNCHULA, oen. nov. 



Page 181. 



Orthokhynchula Linneyi. Nettelrotli. 



Figs. 10-12. Dorsal, pi-ofile and ventral views of the exterior of an average example; showing contour and 



character of plication. 

 Fig. 13. The central portion of the cardinal i-egion, enlai-ge<l ; showing the sharply defined cardinal area 



and the open delthyrium. X 3. 

 Fig. 19. The interior of a pedicle-viilve ; showing the obscurely defined muscular impre.ssion, the cardinal 

 area, open delthyrium and teeth. The area has been encroached ujion by the delthyrium and 

 consequently diminished in size. 



Hudson River group. NasJwille, Tennessee. 

 The original specimens of this species are fi'om Danville and neigboring localities, Kentucky. 



Genus RHYNCHOTREMA. Halt. 



Papre 182. 



Rhynchotrema capax, Conrad. 



Figs. 14, 15. Dorsal and fi-ontal views of a .somewhat gibbous adult ; showing the chai-acter of the plication 

 and the fine concentric lineation. 



Hudson River group. Frankfort, Kentucky. 



Fig. Ifi. The interior of a pedicle-valve ; showing the thickened lieltidial plates consolidated with the 

 valve, the deep pedicle and muscular cavity, and recurved teeth. 

 Hudson River group. Richmimd, Indiana. 



Fig. 17. The interior of a pedicle- valve; .showing the bi-oad, concave deltidial plates, in (contact for their entire 

 length along the median line, greatly thickened and consolidated with the bottom of the valve 

 beneath ; also the recurved teeth resting upon the thickened lateral walls, the pair of shallow 

 depressions in the nmbonal region and the ileep di<iuctor scar in the middle of the valve, which 

 has been greatly encroached upon by the umbonal thickening of the shell. 



Fig. 18. An enlargement of the umbonal portion of the same specimen. The small cavity at the base of the 

 lieltidial plates is the inner opening of the pedicle-passage which was functional at this advanced 

 growth-stage of the shell, its outer opening being on the back of the umbo, considerably 

 removed from the beak, and connected with the apex by a groove whose margins are shown 

 in the figure. (For more complete illustration of this structure, see supplementary plate.) 



Fig. 20. The interior of an incomplete brachial valve ; .showing the hinge-plate, cardinal process and 

 median septum. 



