132 PALEONTOLOGY OF THE EUEEKA DISTEIOT. 



served in P. (P.) Shumardianus, and, as it occurs in Nevada, it is very 

 distinct from the young shells of the latter species. It approaches much 

 more nearly P. (P.*) navicella, with which it is associated, differing from that 

 very decidedly in its truncated apex, much less arcuate ventral valve, and 

 broader, less elongate outline. With Productus Murchisonianus it appears 

 to present but very few characters in common 



Formation and localities. Lower horizon of the Devonian limestone, 

 south ridge of Atrypa Peak, and west slope of County Peak, Eureka Dis- 

 trict, Nevada. 



Frodnctus (Productella) lachrymosus var. limus Conrad (Sp.). 



Plate xiii, figs. 18, 18 a. 



Strophomena lima Conrad, 1842. Jour. Acad. Nat. Sci. Pliilad., vol. viii, p. 256. 

 Productella lachrymosa var. lima Hall, 1867. Pal. N. Y., vol. iv, p. 174, pi. xxv, figs. 

 29-32. 



This variety of P. (P.) lachrymosus is well represented by specimens from 

 the summit of the Devonian limestone at The Gate, where it is associated 

 with P. (P.) subacukatus and P. (P.) lachrymosus var. stigmatus. The median 

 depression of the ventral valve and the characters of the spiniferous tuber- 

 cles are distinctly marked, as also the general form and size of the shell. 



Formation and locality. Devonian limestone, at The Gate, northwest of 

 Eureka, Nevada. 



Productus (Productella) lachrymosus, var. stigmatus Hall. 



Productella lachrymosa var. stigmata Hall, 1867. Pal. N. Y., vol. iv, p. 174, pi. xxv, 



figs. 33-41. 

 Compare Productus f Meek, 1868. Trans. Chicago Acad. Sci., p. 92, pi. xiii, fig. 5. 



This strongly marked variety is represented by a fine series of speci- 

 mens that present it as fqund in the Chemung Group of New York and also 

 pass towards a more costate variety that, in this respect, draws near the true 

 species P. (P.) lachrymosus, but in size and general appearance it is more 

 nearly related to the var. stigmatus. The costse or plications are not formed 

 by the elongation of the spine bases but by the plication of the shell, and 



