294 



NORTH AMERICAN INDEX FOSSILS. 



depressed line. Differs from Uncinulus micleolatits externally in 

 having stronger plications. 



Helderbergian (Becraft) of New York. 



Fig. 365. Wilsonia ventricosa (Pal. N. Y., III.). 



LXXXI. Hypothyris King. 



Subcuboidal, with plications. Similar to Uncinulus but muscu- 

 lar scars of pedicle valve are small and faint and the septum in 

 brachial valve is very faint. Devonic. 



273. H. emmonsi (Hall and Whitfield). Middle Devonic. 



Squarely truncate in front. Pedicle valve depressed-convex; 

 beak small, projecting; median sinus very broad, at front abruptly 

 bent upward in a broad linguiform extension nearly equal to the 

 entire height of the shell and about two thirds as wide as the width 

 of the shell ; the sides of this extension are straight and parallel 



Fig. 366. a-d y Hypothyris cuboides (Pal. N. Y., IV.); e-f, Pitgnax pugnus (Pal. 

 N. Y , IV.) ; g-h, Pugnax grosvenori (Ind. Geol. Survey). 



almost to the top. Brachial valve very convex. Surface marked 

 by about 25 low rounded plications on each side of the mesial fold 

 and sinus with about 14 in each of the latter. 

 Iowa, Nevada, Athabasca. 



