130 PALEONTOLOGY OF THE EUREKA DISTRICT. 
closely allied and probably identical species. This form ranges throughout 
the Devonian limestone of the district and occurs in the lower beds at Lone 
Mountain, 18 miles northwest of Eureka. 
The variety P. (P.) pyxidatus is found in both the lower and upper 
beds. It does not appear to be specifically distinct from the form referred 
to P. (P.) Shumardianus. 
Productus (Productella) Hallanus, n. sp. 
Plate xiii, figs. 17, 17a. 
Productus dissimilis Hall, 1858. Geol. Rep. Iowa, vol. i, pt. 2, p. 497, pl. iii, figs. 7a-e. 
dissimilis Meek, 1868. Trans. Chicago Acad. Sei., vol. i, p. 91, pl. xiii, fig. 3. 
Not Productus dissimilis De Koninck, 1846. 
Shell semielliptical or suborbicular, with the length and breadth 
usually nearly equal, although in some instances it is transversely ellipti- 
cal. Hinge line shorter than the greatest width of the shell 
Ventral valve strongly convex, ventricose on the upper part, which 
projects slightly over the hinge line at the umbo and terminates in a slightly 
incurved beak; the sides are a little depressed towards the somewhat auric- 
ulate cardinal extremities. Area extremely narrow and rarely seen even on 
well preserved shells. Dorsal valve concave, following the curvature of 
the opposite valve. 
Surface of ventral valve marked by fine radiating strize that are slightly 
irregular in their course, as if deflected by the few scattered, scarcely per- 
ceptible spine bases. The dorsal valve shows no radiating striz, but strong 
subimbricating, concentric lines give a striking appearance in constrast with 
the radiating striee of the ventral valve. 
The type specimens of Professor Hall’s P. (P.) dissimilis were from 
the Hamilton Group, at or near Rockford, Iowa, and present all the char- 
acters mentioned in the above description, which was drawn from the 
Nevada specimens. The specific identity of the two forms is very close, 
and does not permit of a separation on any differences presented by the 
specimens now before me. As the name given by Professor Hall was pre- 
occupied by a species of the same generic relations from the Devonian 
