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 \ 7 ariety 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. 



Froductus (Productella) Hallanus, n. sp. 

 Plate xiii, figs. 17, 17a. 



Productus dissimilis Hall, 1858. Geol. Sep. Iowa, vol. i, pt. 2, p. 497, pi. iii, figs. 7a-e. 

 dissimilis Meek, 1868. Trans. Chicago Acad. Sci., vol. i, p. 91, pi. 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 stria3 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 stria?, but strong 

 subimbricating, concentric lines give a striking appearance in constrast with 

 the radiating striae 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 



