Figs. 20, 21. Ventral and dorsal views of an internal cast of conjoined valves; 
showing, in figure 36, the impression of the pedicle muscle, the 
diductor and adductor scars bounded by divergent ridges, and, in 
figure 87, the cast of the delthyrial cavity and the. extent of the 
median septum. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
STENOSCHISMA, Conran. 
Page 826, 
STENOSCHISMA FORMOSA, Hall. 
Figs. 22, 28. Dorsal and profile views of the exterior. 
Fig. 24. Enlargement of the hinge-plate; showing its deep median division, 
minute cardinal process, flat crural lobes and concave crura. X 4. 
Lower Helderberg group. Albany county, N. Y. 
CYCLORHINA, Hatt. 
Page 830. 
CyYcLoRHINA NoBILis, Hall. 
Figs. 25, 26. Dorsal and ventral views of a young shell; showing the obtuse 
umbones, deeply truncated beak, straight cardinal line and low 
median fold and sinus. 
Figs. 27, 28. Front and cardinal views of a mature individual. 
Hamilton group. Thedford, Ontario. 
Fig. 29. The interior of a pedicle-valve; showing the teeth and the scars of the 
pedicle, adductor and diductor muscles. 
Fig. 30. A weathered specimen; showing the cavities occupied by the crura. 
Hamilton group. Darien, N. Y. 
Fig. 31. An enlargement of the external surface; showing the fine concentric 
lines which crenulate the crest of each plication. X 3. 
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