NIAGARA FALLS AND VICINITY 205 



Distinguishing characters. Subcircular; gibbous; strongly con- 

 vex pedicle valve with deep median fur- 

 row, deepening and widening forward; 

 frontal linguiform elevation, obtuse cari 

 nated fold in sinus; strong fold on brachial 

 valve, with a lateral fold on each side more 



1 ■ . Fig. 121 Hyattella eongesta 



or less prominent. 



Fig. 131a Hyattella eongesta 



Found in the lower Clinton limestone at Niagara. Also at Lock- 

 port (Hall). 



Genus anoplotheca Sandberger 



[Ety. : clvo-Zos, unarmed; Oyjxrj, sheath] 



(1853. Sitzb. d. K. K. Akad. d. Wissens. math, naturw. Classe, 

 16, p. 5, 18, 102; 1894. Hall & Clarke. Pal. N. Y. v. 8, pt 2, p. 129) 



Concavo-convex, small shells with few plications crossed by fine 

 often imbricating growth lines. Brachial valve with a high median 

 septum. Brachidium a pair of spiral cones, as in Wh.it- 



-■ — -i*^— ■ .-. ■ . f i e 1 d e 1 1 a . 



r 



Anoplotheca hemispherica (Sowerby) 

 , (Fig. 132). Atrypa hemispherica 

 f Hall (1852. Pal. N. Y. 2:74, pi. 23) 



Distinguishing characters. Hemispheric 

 to semiorbicular form; nearly flat brachial 

 valve, convex pedicle valve; extended, 

 nearly straight hinge line; eight to 12 



Fig. 132 Anoplotheca hemispherica J ° ° ° 



with striae enlarged rounded to subangular, simple plications; 



strong, undulating concentric striae. 



Found poorly preserved in the Clinton shale at Niagara. 



Anoplotheca plicatula (Hall) (Fig. 133). Atrypa plicatula 

 Hall (1852. Pal. N. Y. 2:74, pi. 23) 



Distinguishing characters. Slightly wider than long or sub- 



