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, pi. xxxiii, figs. 2J-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, pi. xiv, figs. 1 a-c and 2 a-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. (M.) 

 meristoides, and the form of S. (M.} meristoides is similar to that of a globose, 

 elongate variety of 8. (-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 

 striae 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 8. (M.) Maia. At first these were separated and referred to S. (M.) 

 subumbona, but the obtaining of a large number of specimens of various 

 forms and size in association with S. (M.} Maia showed this separation to 

 be a forced one. It is possible that S. (M.) 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. (M.} 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. 



