Fig. 11. A cast of the hinge-plate; showing the unbroken filling of the visceral 
canal. 
Oriskany sandstone. The Helderbergs, N. Y. 
RENSSELHRIA OvoIDES, Haton. 
Fig. 12. An interior cast of the brachial valve; showing the cavity of the 
hinge-plate, the branching vascular sinuses in the umbonal region 
and the anterior and posterior divisions of the adductor muscular 
impression, the surface of the posterior scars being strongly marked 
with ramifying lines. The structure and arrangement of all of 
these parts is strikingly similar to that occurring in AMPAIGENIA. 
Oriskany sandstone. Schoharie, N. Y. 
Fig. 13. The exterior of a pedicle-valve, having the characteristic inflexion 
of the lateral margins anteriorly, and showing the fine surface 
plication. 
Fig. 14. Profile of conjoined valves; showing the usual convexity of the spe- 
cies. The shell of the brachial valve has been exfoliated, losing its 
surface plication. ; 
Oriskany sandstone. The Helderbergs, N. Y. 
RENSSELZRIA OvULUM, Hall. 
Fig. 15. An internal cast of the pedicle-valve; showing the filling of the deep 
muscular cavity and its division by the diductor and adductor ~ 
scars, and the cavities left by the teeth. This species differs from 
the foregoing in its persistently greater size, much more convex 
valves, and coarser plication of the surface, It is a more orbicular 
and more regularly convex shell than R. ovoides. 
Oriskany sandstone. Cayuga, Ontario. 
259 
