PLATE XII— Continucil. 



Strophonella re versa, Hall. 



Fig. 16. View from the lirai-hial valve; showing the iiiiinteirupteci ai-ea of the ))edio.le-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 scars. 



Fig. 19. The iiiterior of a pedicle-valve in which the muscular and viiscular m.arkings ai'e vei'y strong. 

 The cardinal area is seen to lie without any trace of deltidiuni, and the unibonal cavity has 

 been so completely tilled by calcareous depositions about the lobes of the cardinal proc-ess that 

 the latter have broken and remain attached (i. i,) to the pedicle-valve. 



Fig. 2(1. The central portion of the hinge, enlarged, from .a specimen which has lieen somewhat weathei-ed, 

 thus exposing the vertical ridges which terminate in crenulations at the margin, anil .also show- 

 ing the limits of the deltidia. X 2. 



Upjier Devonian. Roekford. Iowa. 



Strophonella c^lata. ILiU. 



(See Plate XVb, tig 10.) 

 Fig. 21. A cast of the interior of the pedicle-valve ; showing the widely extended, crenulated hinge-iine. and 

 the very concave valve with strong luuscular and vascular impressions. The points marked k, 

 are the tilling of the cavities beneath the area for receiving the extremities of the i-ardinal 

 process. 



Chemung group. Near Elmira, N. Y. 



