NIAGARA • FALLS AND VICINITY 209 



Found in a loose block of limestone, probably the lower Lock- 

 port limestone, at Niagara. One specimen. 



The identification with Hall's species and the generic reference 

 -are provisional. 



Genus MODioLopsisHall 



[Ety. : Modiolus, a genus of recent shells; dcpcg, appear- 

 ance (similar to)] 



(1847. Pal N. Y. 1:157) 



Shells equivalve; valves elongate oval, closed, with nearly ter- 

 minal beaks and narrow hinge plate, and without teeth; adductor 

 scars subequal; ligament deep-seated. 



Modiolopsis orthonota (Conrad) (Fig. 137) (Hall. 1852. Pal. 

 N. Y. 2:10, pi. 4 bis) 



Distinguishing cJiaractcrs. Subelliptic or 

 rhomboidal form; straight hinge line; obliquely 

 truncated anterior and rounded posterior ends; 

 ventral. and dorsal margins nearly parallel; ele- 

 vated, thin, sharp umbones, with a faint ridge 

 extending to the posterior basal margin; sur- Fig . 137 Modiolopsis ortho . 

 face with concentric growth lines only. 



Found in the upper Medina sandstones at Niagara. Also in the 

 same beds at Lockport, usually as molds. 



Modiolopsis primigenia (Conrad) (Fig. 138) (Hall. 1852. Pal. 

 N. Y. 2:10, pi. 4 bis) 



Distinguishing characters. Subrhomboidal form; rounded anterior 

 and expanded alate posterior ends; straight 

 hinge line, produced posteriorly; rounded ven- 

 JW tra ^ mar gi n ; fi n e radiating striae visible only 

 -:.i>-., -^ - i n we u preserved shells; strong concentric 



Fig. 13S Modiolopsis primi- g r OW.th lines. 



Found usually as internal molds, in the upper 

 Medina sandstones of the Niagara sections, and at Lockport and 

 elsewhere. 



Modiolopsis sp. (Compare M. subalatus. Pal. N. Y. 2:84, 

 pi. 27, fig. 5, 6; p. 285, pi. 59, fig. 7) 



Distinguishing characters. A small left valve, strongly convex 

 below the umbo; a strong cardinal ridge extends from beak to pos- 



