FOSSILS OF THE CARBONIFEROUS. 243 
Genus MACRODON Lycett. 
Macrodon Hamiltone Hall. 
Plate xxiii, figs. 5, 5a-c. 
Macrodon Hamiltone Hall, 1870. Prelim. Notice Lam, Shells, 8vo., pamphlet, p. 13. 
Idem., 1883. Pal. N. Y., vol. v, pt. 1; Plates and Explanations, pl. li, figs. 
1-10. 
In comparing a large series of specimens referred to this species from 
Nevada, with the beautiful illustrations of it given in the Paleontology of 
New York, and also with specimens from the Hamilton Group of New York, 
I do not find sufficient differences on which to base a specific separation 
of the Nevada and New York shells, although the former occur in strata of 
Lower Carboniferous age, and the latter in the lower half of the Devonian 
Group. The differences are in the outline of the cardinal margin as com- 
pared with the majority of the New York specimens, and the apparently 
thicker shell. -The first is negatived by the occurrence of specimens of the 
same outline with the New York specimens, and the second is owing to the 
condition of preservation, the macerated, compressed shells of the Hamilton 
shales not preserving the original structure of the shell. The Nevada speci- 
mens show the large anterior muscular scar in the casts, but not the lateral 
teeth shown in many of the New York examples of the species. 
Formation and locality—Lower portion of Lower Carboniferous lime- 
stone in canon directly south of a small conical hill on east side of Secret- 
canon-road Canon, Eureka District, Nevada. 
Macrodon truncatus, n. sp. 
Plate viii, fig. 2. 
Shell subrhomboidal, convex, with an undefined depression extending 
from the beak obliquely to near the center of the basal line; anterior side 
rounded, posterior side rounded below, nearly straight above. Hinge-line 
straight, nearly as long as the greatest width of the shell below. Umbo 
depressed, situated anterior to the middle of the valves; beak small, in- 
curved. 
