PLATE XII— Continued. 



Strophonella reversa, Hall. 



Fig-. 16. View from tlie bj-achial valve ; siiowing tlie uninterrupted area of tlie pedicle-valve. 



Fig. 17. The extei-ior of the pedicle-valve. 



Fig. 18. The interior of a l)rachial valve ; showing the deeply bifurcated cardinal process and the muscu- 

 lar scai-s. 



Fig. 19. The interior of a pedicle-valve in which tlie muscvilar and vascular markings are very strong. 

 The cardinal ai'ea 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 proce.ss that 

 the latter have bi'oken and I'emain 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 tei'minate in crenulations at the margin, an<i also show- 

 ing the limits of the deltidia. X. 2. 



Upper Devonian. Rockford, Iowa. 



Strophonella cjelata, Hall. 



(See Plate XVb, tig 10.) 

 Pig. 21. A cast of the interior of the pedicle-valve ; siiowing the wi(Jely extended, crenulated hinge-line, and 

 the vei'y concave valve with strong muscular and vascular impressions. The points marked k, 

 are the filling of the cavities beneath the area for receiving the exti'eniities of the cardinal 

 process. 



Chemxing group. Near Elmira, N. Y. 



