FOSSILS OF THE DEVONIAN. 247 



dorsal valve marked by fine, even striae. The specimen measures about 

 seven-eighths of an inch in length by a little more than an inch in width; 

 convexity of the ventral valve about five-sixteenths of an inch. 



The specimen possesses all the essential specific characters of the Iowa 

 shells, but difiers slightly in the more decidedly quadrangular outline. This 

 feature alone, however, cannot be considered of specific importance, since, 

 among the typical specimens, the variation in this respect is considerable. 



Formation and locality. — In limestone of Devonian age, at Treasure Hill, 

 south of Aurora Mine, White Pine, Nevada. Collected by Arnold Hague, 

 esq. 



Genus RHYNCHONELLA Fischer. 



Ehykchonella Emmonsi n. sp. 



Plato III, figs. 4-8. 



Shell rather above the medium size, globosely subcuboidal, very ven- 

 tricose, highly gibbous on the dorsal side, shallow and somewhat flattened 

 on the ventral and squarely truncate in front; cardinal margin broadly 

 rounded, the small, pointed, ventral beak projecting beyond the general con- 

 tour, and having the appearance of a small cardinal area from the projection 

 of the margin of the foramen, into which the beak of the dorsal valve passes; 

 sides of the shell more sharply rounded than the cardinal border. Front of 

 the ventral valve abruptly bent upward in a broad, linguiform extension, 

 nearly or quite equal to the entire height of the shell, and almost two-thirds 

 as wide as the entire width; the sides of the extension are straight and 

 parallel for most of the height, the top being broadly and evenly rounded. 

 Dorsal valve emarginate in front, corresponding with the extension of the 

 ventral valve. 



Surface marked by from twenty-three to twenty-five low, rounded, 

 simple plications on each side of the elevation and sinus, and about fourteen 

 on the elevation of the dorsal valve, with a corresponding number on the 

 extension of the ventral A^alve. 



The species is of the type of R. cuhoides of Europe and R' venusta Hall, 

 of the Tully limestone of New York. It differs from the former in its much 

 less cuboidal form and broader and shorter proportions, and from the latter 



