122 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Strophodonta Calvini Miller. 
Plate xiii, fig. 6. 
Strophodonta quadrata Calvin, 1878. Bull. U. S. Geol. Survey, vol. iv, p. 728. Not 
of Swallow, 1860. Trans. St. Louis Acad. Sci., vol. i, p. 639. 
Calvini Miller, 1883. Cat. Amer. Pal. Foss., 2d ed., p. 298. 
The author describes this species as follows: 
“Shell small, concavo-convex, quadrate in outline. Cardinal extremi- 
ties sometimes abruptly produced, sometimes rounded. Ventral valve very 
convex, flattened on the umbo and descending rapidly to the lateral and 
frontal margins. Dorsal valve concave, following closely the curvature of 
the other. Hinge area common to both valves, wider on ventral, finely 
striated. Foramen only sufficiently developed to receive the extremities of 
the bifid cardinal process. Muscular scars faintly impressed, not definitely 
bounded. 
" “Surface of ventral valve ornamented by fine radiating striz. From 
three to five very small strize are implanted between pairs of more promi- 
nent, but very slender, filiform, and often slightly interrupted ones. A 
broad, shallow mesial sinus sometimes occupies the front half of the valve. 
On the dorsal valve the strize are subequal, corresponding to the finer ones 
of the ventral valve. 
“Length, 9™"; width, 11™"; convexity, 5™™.” 
The species occurs in the Devonian formation of Iowa and corresponds, 
from the description, very closely with the Nevada form. The latter is pro- 
portionally a little broader and slightly convex on the umbo, but does not 
appear to differ specifically. 
Formation and l6calities—Lower horizon of the Devonian limestone, 
Lone Mountain, 18 miles northwest of Eureka, and Comb’s Peak, Eureka 
District, Nevada. 
Genus CHONETES Fischer. 
It is difficult to determine the specific relations of many of the forms 
of the Productide and especially those belonging to the genus Chonetes, 
as the shells are usually small and depend largely on the surface characters 
and the presence of the cardinal spines for their specific determination. 
