136 PALEONTOLOGY OF THE EUREKA DISTRICT, 



Spirifera varicosa Hall. 



Spirifer vaticosus Hall, 1857. Tenth Ann. Rep. N. Y. State Cab. Nat. Hist., p. 130. 



Ibid., Description of New Pal. Fossils, p. 90, 1857. 

 Spirifera varicosa Hall, 1867. Pal. New York, vol. iv, p. 205, pi. xxxi, figs. 1-4. 



Ventral valve transverse, semielliptical ; length less than one-half the 

 width, lateral extremities pointed; strongly convex, most prominent on the 

 umbo; mesial sinns strongly defined, rounded on the bottom and continued 

 to the apex of the beak; beak narrow and slightly incurved. Area equal 

 to one-half the width of the valve; it is flat below and a little concave 

 towards the apex; the fissure is high and large. 



Surface marked by eight or nine simple, slightly angular plications on 

 each side of the mesial sinus, and with fine radiating stria? near the umbo, 

 where the only fragment of the outer surface is preserved, the remaining 

 portions having been entirely exfoliated; traces of strong concentric striae, 

 however, are seen on the lower part of the cast. 



The species represented by this single valve, is a member of a group 

 of species illustrated by Spirifera varicosa, S. segmenta, and 8. arctisegmenta, 

 in the Upper Helderberg limestones of the Falls of the Ohio, and in New- 

 York State. It is related to S. varicosa by the general form, the size of the 

 area and foramen, and the number of surface plications, and also the fine 

 radiating striae near the umbo; but, in the absence of the strong varicose 

 concentric stria?, a striking difference exists between them. In the character 

 of the plications the agreement is with S. arctisegmenta, but the latter has a 

 very narrow foramen and the area bending forward, features that lead to 

 making a provisional reference to the former species, as they are considered 

 as of more importance than the development of the surface stria?; besides 

 the Nevada shell shows traces of strong concentric stria? on the cast, and a 

 large series of specimens would probably exhibit considerable variation in 

 this respect. In this event, or should it prove to be a distinct species, it adds 

 another member, by its general character, to the group of forms uniting the 

 fauna of the Lower Devonian of Nevada and that of the Upper Helderberg 

 Group east of the Rocky Mountain region. 



Formation and locality. Lower portion of the Devonian limestone, at 

 Lone Mountain, 18 miles northwest of Eureka, Nevada. 



