136 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Spirifera varicosa Hall. 
Spirifer varicosus 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, pl. 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 sinus 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 striz near the umbo, 
where the only fragment of the outer surface is preserved, the remaining 
portions having been entirely exfoliated; traces of strong concentric striz, 
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 S. 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 strize near the umbo; but, in the absence of the strong varicose 
concentric striz, 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 striz; besides. 
the Nevada shell shows traces of strong concentric striz: 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. 
