142 PALEONTOLOGY OF THE EUREKA DISTRICT 
specimens representing the young of S. (M.) Maia in the collections from Res- 
cue Hill and Sentinel Mountain. Those that are broader than long, with the 
beak a little incurved over the high, prominent area of the ventral valve, 
are essentially identical with the type specimens illustrated by Professor 
Hall (Pal. N. Y., vol. iv, pl. xxxiii, figs. 22-30) from the Hamilton Group 
of New York as Spirifera (M.) subumbona. Closely resembling these come the 
forms described by Mr. Meek from the Devonian limestone of the Macken- 
zie River Basin. As described by him and illustrated (Trans. Chicago 
Acad. Sci., pp. 103, 106, pl. xiv, figs. 1 a—c and 2a-c), the two species S. 
(M.) meristoides, and S. (M.) sublineatus, appear to be identical with the 
New York and Nevada species. The muscular impression on the cast of 
the ventral valve shows the faint furrow in some specimens more deeply 
impressed, with the flat, shallow, lateral impressions, as in S. (M.) sublineata, 
and in other specimens the vascular impressions are shown, as in S. (JL) 
meristoides, and the form of S. (A.) meristoides is similar to that of a globose, 
elongate variety of S. (M.) Maia, that has the beak closely incurved. If 
the species are not the same they are at least very closely allied. The 
series of variations continue in the direction of a more elongate gibbous 
form, with the beak incurved over and partially concealing the low area; 
this feature also occurs in a broader gibbose variety, which is connected by 
a direct series of specimens with the Hamilton species S. (M.) subumbona. 
The latter, as it occurs in New York, is distinguished by the fine concentric 
strize and minutely punctate surface, although the shell structure appears to 
be fibrous. The same surface and shell structure is shown in the young 
shells of S.(L.) Maia. At first these were separated and referred to S. (J/.) 
subumbona, but the obtaining of a large number of specimens of various 
forms and size in association with S. (JZ.) Maia showed this separation to 
be a forced one. It is possible that S. (JZ) subumbona is distinct from the 
young of S. (M.) Maia, and until the material can be obtained to show 
that in the eastern Devonian the young of S. (.) Maia is identical with S. 
(M.) subumbona, the two specific names will have to be recognized. 
Formation and localities—Devonian limestone, Rescue Hill, south 
slope of Sentinel Mountain, west slope of County Peak, Eureka District 
and Lone Mountain, northwest of Eureka, Nevada. 
