PLATE LVI. 



(Plgares 1-13, 16-28, 28-34, 36,37, 45 by G. B. Simpson; U, 15, 24-27 by R. P. Whitfield; 85, 38 by C. E. Beeches; 



39-44 copies.) 



Genus RHYNCHONELLA, Fischer de Waldheim. 



Page 177. 



Rhynchonella loxia, Fischer de Wiildheim. 



Figs. 1-5. Doi-sal, ventral, pi-ofile, frontal and cardinal views of a normal mature individual, retaining the 

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

 plication. 

 Fig. 6. Cardinal view of an internal cast ; showing the cavity of the dental plates and median septum. 

 This is the type of the genus Rhtnchonklla. 



Upper Jurassic. Okaraschowa, Russia. 



Genus PROTORHYNCHA, gen. xov. 



Pago 180. 



Protohhyncha ^quiradiata, Hall. 



Fig. 7. An iatemal 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 cai-dinal area, 

 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 pedicle-valve ; showing a well defined median sinus and a very re- 

 stricted muscular scar in the umbonal i-egion. X 2. 

 Clinton group. New Hartford, N. T. 



Genus ORTHORHYNCHULA, oen. nov. 



Page 181. 



Orthorhynchula Linneyi, Nettelroth. 



Fig8. 10-12. Dorsal, profile and ventral views of the exterior of an average example; showing contour and 



character of plication. 

 Fig. 13. The central portion of the cardinal region, enlarged ; showing the sharply defined cardinal area 



and the open delthyrium. X 3. 

 Fig. 19. The interior of a pedicle-valve ; showing the obscurely defined muscular impression, the cardinal 

 area, open delthyrium and teeth. The area has t)een encroached upon by the delthyrium and 

 consequently diminished in size. 



Hudson River group. Nashville, Tennessee, 

 The original specimens of this species are from Danville and neigboring localities, Kentucky. 



Genu8 RHYNCHOTREMA. Hall. 



PaifC 182. 



Rhynchotrema capax, Conrad. 



Figs. 14, 16. Doraal and frontal views of a somewhat gibbous adult; showing the character of the plication 

 and the fine concentric lineation. 



Hudson River group. Frankfort, Kentucky. 



Fig. 16. The interior of a pedicle-valve ; showing the thickened deltidial plates consolidated with the 

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

 Hudson River group. Richmond, Indiana. 



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

 length along the me<lian 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 umbonal region and the deep diductor scar in the middle of the valve, which 

 has been greatly encroache<i 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 

 deltidial 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. 



