RHYNCHOTREMA, Hatt. 
Page 825. 
RayYNCHOTREMA CAPAX, Conrad. 
Figs. 11, 12. Dorsal and front views of a somewhat gibbous adult; showing 
the character of the plication and the fine concentric lineation. 
Hudson River group. Frankfort, Kentuciy. 
Fig. 18. The interior of a pedicle-valve; showing the broad, 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 umbonal region and 
the deep diductor scar in the middle of the valve, which has been 
greatly encroached upon by the umbonal thickening of the shell. 
Fig. 14. 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. 
Fig. 15. An enlargement of the umbonal portion of a brachial valve; show- 
ing the deflection of the vertical septiform cardinal process, the 
character of the hinge-plate, socket-walls, sockets and crural 
apophyses. 
Figs. 13, 14, 15 are:from the specimens upon which the characters of the 
genus were originally established. 
Hudson River group. Jron Ridge, Wisconsin. 
Fig. 16. The interior of an old brachial valve: showing the deflection of the 
cardinal process and the thickened hirge-plate. 
Hudson River group. Richmond, Indiana. 
RHYNCHOTRETA, Hatt. 
Page 825. 
RaYNCHOTRETA CUNEATA, Dalman, var. AMERICANA, Hall. 
Figs. 17, 18. Dorsal and profile views of an average example; showing the 
contour of the shell and the character of the plication. 
Niagara group. Waldron, Indiana. 
Fig. 19. The cardinal region of an adult specimen, enlarged, showing the 
unusual size of the deltidial plates, their outward flexion along the 
median suture, the apical and encroaching position of the foramen. 
x 5. (BEECHER and CLARKE.) 
Niagara group. Waldron, Indiana. 
240 
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