PLATE XII—Continued. 
Strophonella re versa, Hall. 
Fig. 16. View from the brachial valve; showing the uninterrupted area of the pedicle-valve. 
Fig. 17. The exterior of the pedicle-valve. 
Fig. 18. The interior of a brachial valve ; showing the deeply bifurcated cardinal process and the muscu¬ 
lar seal's. 
Fig. 19. The interior of a pedicle-valve in which the muscular and vascular markings are very strong. 
The cardinal area is seen to be without any trace of deltidium, and the umbonal cavity has 
been so completely filled by calcareous depositions about the lobes of the cardinal process that 
the latter have broken and remain attached ( i, i,) to the pedicle-valve. 
Fig. 20. The central portion of the hinge, enlarged, from a specimen which has been somewhat weathered, 
thus exposing the vertical ridges which terminate in crenulations at the margin, and also show¬ 
ing the limits of the deltidia. X 2. 
Upper Devonian. Rockford, Iowa. 
Strophonella c^ilata, Hall. 
(See Plate XVb, fig. 10.) 
Fig. 21. A cast of the interior of the pedicle-valve ; showing the widely extended, crenulated hinge-line, and 
the very concave valve with strong muscular and vascular impressions. The points marked k, 
are the filling of the cavities beneath the area for receiving the extremities of the cardinal 
process. 
Chemung group. Near Elmira, N. Y. 
