35Q 



NORTH AMERICAN INDEX FOSSILS. 



405. A. (Coelospira) hemispherica (Sowerby). (Fig. 455.) 



Siluric. 



Hemispheric. Brachial valve flat. Hinge line nearly straight. 

 Surface marked by 8 to 12 or more rounded, simple plications 

 which are crossed by strong concentric growth lines. 



Clinton of New York, Kentucky, Tennessee, Georgia, Alabama, 

 Nova Scotia, Anticosti. 



406. A. plicatula (Hall). (Fig. 456.) Siluric. 





Fig. 455. Anoplotheca hemispherica FiG. 456. Anoplotheca plicatula (Pal. 

 with strke enlarged (Pal. N. Y., II.). N. Y., II.). 



Small, ovate. Valves subequal. Pedicle valve slightly carinate 

 at umbo, with a slight median sinus anteriorly. Brachial valve 

 almost flat toward the beak and elevated into a median fold an- 

 teriorly. Surface with two plications in sinus and three on fold 

 with six to eight on each side. Concentric striae not conspicuous. 



Clinton of New York and Niagara of Wisconsin. 



407. A. concava (Hall). Devonic. 



Pedicle valve convex. Brachial valve flattened near lateral mar- 

 gins and at times depressed in the middle due to the rapidly 

 widening sinus. Surface marked by rounded striae ; the one on the 



Fig. 457. Anoplotheca {Leptocoelia) Jlabellites (Pal. N. Y., IV.). 



mesial fold is generally smaller than the others giving the fold a 

 slightly grooved appearance along its center quite to the beak. 



Helderbergian of New York, and of Kennedy channel in Arctic 

 region. 



