NIAGARA FALLS AND VICINITY 1 89 



Distinguishing characters. Nearly circular and equivalve; finely 

 striated surface; dichotomous striae running upward and outward 

 on the hinge line; narrow short hinge area; slightly sinuous front. 



Found in the lower Clinton limestone (?). Also east of Lockport 

 (Hall). 



Genus scenidium Hall 



[Ety.: ezyvidov, little tent] 



(i860. N. Y. state cab. nat. hist. 13th reft, p. 70; 1892. Pal. N. Y . 



v. 8, pt 1, p. 241) 



Shells subpyramidal, somewhat semicircular; with or without 

 median sinus or elevation; pedicle valve elevated, subpyramidal; 

 beak straight or slightly arched; cardinal area large, triangular, di- 

 vided by a narrow fissure, sometimes closed at the summit by a con- 

 cave plate. Brachial valve depressed convex to concave; cardinal 

 line usually equal to width of shell; cardinal 

 process simple or divided, and extending as a £" 

 median septum through the length of the shell. 

 Spondylium in the pedicle valve. 



Scenidium pyramidale Hall (Fig. 100). Or- 

 t h i s pyramidale Hall (1852. Pal. 



A. 1 . 2:251, pi. 52, fig. 2a-z) Fig. 100 Scenidium pyramid- 



„ . • 7 • 7 -v r • a ^ e eulargecl 



Distinguishing characters. Minute, subpyra- 

 midal; fiat semicircular brachial valve, centrally depressed; ex- 

 tremely elevated pedicle valve with large triangular area; strong 

 radiating striae, sometimes dichotomous; lamellose concentric 

 striae. 



Found in the Rochester shale at Lockport (Hall) and may also 

 occur at Niagara. 



Genus anastrophia Hall 



[Ety.: avd, back; <7rpo<p-/j, a turning] 



(1867. A r . Y. state cab. nat. hist. 20th an. reft, p. 163; 1893. Pal. 



N. Y. v. 8, pt 2, p. 224) 



Pentameroid shells with a spoon-shaped cavity (spondylium) 

 under the beak of the pedicle valve and with a moderate cardinal 

 line but no hinge area; surface with numerous sharp plications ex- 

 tending to the beak. 



