FOSSILS OF THE DEVONIAN. 15h 
the Devonian limestone associated with Atrypa recticularis. They are 
readily separated from that species, but not from the young shell of A. des- 
quamata, as illustrated by Davidson, to which they are specifically related. 
The largest specimen has a length of 16™", width of 17", and depth of the 
two valves of 8™. A. desquamata is a much larger and more robust spe- 
cies when fully developed, but the similarity in the young shells of the two 
forms is so strong that we cannot but consider them as specifically identical. 
Formation and localities —Lower horizon of the Devonian limestone, 
Atrypa Peak, south spur; and Lone Mountain, 18 miles northwest of Eu- 
reka, Nevada. 
Genus TREMATOSPIRA Hall. 
Trematospira infrequens, n. sp. 
Plate iv, figs. 3, 3a, b. 
Shell transversely elliptical, moderately convex; hinge about three- 
fourths the width of the shell. 
Ventral valve not quite as convex as the dorsal; mesial sinus well 
defined from the beak to the anterior margin and marked by a single small 
median plication; beak elevated, small, and truncated by a small perfora- 
tion. The dorsal valve has a low mesial fold outlined by two strong plica- 
tions. 
Surface of the ventral valve marked by two strong and one slight pli- 
cation each side of the plication on the edge of the mesial sinus; ventral 
valve by the same number each side of the central plications of the mesial 
fold. Shell structure punctate. 
This is a distinet and well-marked species, approaching Trematospira 
camura Hall, 1852 (Pal. N. Y., vol. ii, p. 273, pl. lvi, figs. 3a-t), of the Niag- 
ara Group and 7. gibbosa Hall, 1867 (Pal. N. Y., vol. iv, p. 272, pl. xlv, figs. 
7-15) of the Hamilton Group of New York more nearly than any other spe- 
cies with which we are acquainted. 
Formation and locality—Lower Devonian, Lone Mountain, 18 miles 
northwest of Eureka, Nevada. 
