FOSSILS OF THE DEVONIAN. 



113 



On a direct comparison with authentic specimens of this species from 

 the Genesee slate of New York, no differences appear that are of specific 

 value. 



Professor Hall says, in comparing D. media of the Hamilton Group of 

 New York with D. Lodensis, that the former may possibly be only a well- 

 marked variety of D. Lodensis (ibid., p. 21). In this I would fully concur. 

 In studying a good series of Discina nitida, as illustrated by Davidson, con- 

 siderable range of variation in convexity, outline, and the position of the 

 apex is apparent, and no doubt other species are subject to as great varia- 

 tions, arising, as they may, from the nature of the local environment during 

 the life of the animal; the character of the sediments and conditions of 

 fossilization. 



Mr. Rathbun identifies this species from the Devonian of Brazil, S. A. 



Formation and locality. Upper Devonian. White Pine shale on the 

 east side of Applegate Canon, White Pine Mining District, Nevada. 



PHOLIDOPS Hall. 



Pholidops bellula, n. sp. 

 Plate ii, figs. 6, 6 a, &. 



Shell minute, broadly oval, depressed; apex eccentric, situated about 

 one-third the distance between the anterior and posterior margins. 



Surface marked by a few fine concentric striae. 



The interior of the dorsal valve presents a rather wide, unbroken mar- 

 gin surrounding the rounded concave interior. Near the center of the shell 

 two oval, slightly-oblique elevated scars occur. No other scars are discern- 

 ible. In the cast Ihe bilobed scars are shown as a rather deep impression, 

 the apex of the shell bein<r entirely truncated. Substance of the shell cal- 

 careous. Average size, 2.5 mm by 2 mm . No ventral valves were discovered. 



In general form this species resembles Pholidops ovalis Hall, (Twenty- 

 eighth Ann. Rep. N. Y. State Mus. Nat. Hist., p, 149, pi. xxi, figs. 1, 2) of 

 the Niagara Group, and P. Hamiltonue Hall (Pal. N. Y., vol. iv, p. 32, pi. iii, 

 figs. 6-9, 1867) of the Hamilton Group of New York. It differs from each, 

 and is specifically distinct from any form with which we are acquainted. 

 8 c D w 



