293 



the ventral somewhat flattened towards the front, very ventricose on 

 the umbo ; beak small and pointed ; area about one-third as hi^h as 

 long , foramen twice as high as wide. Dorsal valve more regularly 

 convex than the ventral, and the beaks less elevated, very small and 

 pointed, but little incurved. 



Surface marked by fine, equal rounded stri«, which are curved 

 upwards near the extremities of the hinge line, and some of them 

 run out on the cardinal border. Increased both by bifurcation and 

 implantation. 



This species differs from 0. Swallovi, Hall (Iowa Geological Kept, 

 Vol. I., Part II., pi. 12, fig. 5), which it most nearly resembles, in the 

 proportionally much greater elevation of the area; and it never 

 attains a size greater than one-third that of full-gi-own individuals of 

 that species. 



Genus Streptorhyxchus, Kino-. 

 Streptorhyxchus ixflatus (n. sp.) 

 ^ Shell above a medium size, somewhat semicircular in outline ; the 

 hinge usually a Httle shorter than the greatest width of the shell, 

 causing a slight rounding of the cardinal extremities. Ventral valve 

 concave in the centre, and elevated at the beak, which is straight and 

 pointed, directed obliquely backward from the hinge line.° Area 

 rather high, irregular in width, and about one-third as high as long ; 

 foramen very narrow, extending to near the point of the b'eak, closed 

 to near the base by a thin, rounded deltidium. Dorsal valve stront^Iy 

 inflated, very prominent on the umbo, a Kttle flattened at the cardinal 

 extremities. 



Surface marked by moderately strong, rounded, somewhat alternate, 

 radiating stri», which present a wiry appearance. The interior of the 

 dorsal valve is characterized by a very large, flabeUiform cardinal 

 process, marked by several strong plications. 



This species differs from S. incequalis (OrtMs incequalis,IIa\l), Iowa 

 Geol. Kept., Vol. i.. Part ii., page 490, pi. 2, fig. 6, with which it is 

 associated, in having a much more ventricose dorsal valve ; in the 

 much greater height of the area of the ventral valve, in which the 

 foramen is about three times as high as wide ; while in that species it 

 is much wider than high. The strias are also coarser, and more 

 elevated. 



Genus Spirifer, Sowerby. 



Spirifer hirtus (n. sp.) 



Shell of medium size, extremely ventricose, about once and a half 



as wide as high. Hinge line very short, not more than one third as 



long as the width of the shell ; front and cardinal angles regularly 



rounded. Ventral valve most ventricose, a httle forward of the beak, 



