FOSSILS OF THE LOWER SILURIAN. 71 
The dorsal valve, fig. 3b, shows a narrow median ridge with a pair of 
minute, elongate, oval scars at its front termination (a, @); posterior to these 
and between the central ridge and a low ridge extending from the beak 
obliquely outward and forward a larger, reniform sear occurs on each side 
(p, @); outside of the narrow lateral ridges and on the posterior lateral por- 
tion of the shell another minute scar is seen on each side (a,d). None of 
the.specimens show a scar beneath the beak. 
A comparison with the figures of Siphonotreta fissa Kutorga® shows a 
strong generic relation, judging from the external characters; specifically 
they have several points in common. 
The species occurs in the passage beds at the base of the Pogonip 
Group in the same band of layers carrying Acrotreta gemma, Lingulepis, 
Discina, Orthis, Camarella calcifera, Ptychoparia Oweni, Dicellocephalus 
Jinalis, Illenurus Eurekensis, Amphion, Barrandia McCoyi, ete. 
Formation and locality—Lower portion of Pogonip Group. East slope 
of ridge east of the Hamburg mine Canon, Eureka District, Nevada. 
Genus STROPHOMENA Rafinesque. 
Strophomena Nemea, H. & W. 
Strophomena Nemea, Hall & Whitfield, 1877. Geol. Expl. Fortieth Par., vol. iv, p. 233, 
pl. i, fig. 15. 
This species occurs in the upper beds of the Pogonip Group at Lone 
Mountain, 18 miles northwest of Eureka, at the same horizon on McCoy’s 
Ridge, and a little lower down in the strata on the west slope of Secret 
Canton road Canon, Eureka District, Nevada. 
The original type of the species is from Pogonip Mountain, White 
Pine District, Nevada. 
6Uber die Brachiopoden-Familic der Siphonotretwx. Verhandl. der Russ. Kais. Mineral. Gesell- 
schaft, 1848, p. 250, pl. vii, figs. 5a-c. 
