FOSSILS OF THE CAEBONIFEEOUS. 



243 



Genus MACRODON Lycett. 



Macrodon Hamiltonae Hall. 

 Plate xxiii, figs. 5, 5o-c. 



Macrodon Hamiltonce Hall, 1870. Prelim. Notice Lain. Shells, 8vo., pamphlet, p. 13. 

 Idem., 1883. Pal. N. Y., vol. v, pt. 1 j Plates and Explanations, pi. 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. 



