FOSSILS OF THE DEVONIAN. 



151 



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 mm , width of 17 mm , and depth of the 

 two valves of 8 mm . A. desquamate 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. 



Geims TREMATOSPIRA Hall. 



Trematospira infrequens, n. sp. 

 Plate iv, figs. 3, 3 a, 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 distinct and well-marked species, approaching Trematospira 

 camura Hall, 1 852 (Pal. N. Y., vol. ii, p. 273, pi. Ivi, figs. 3a-t), of the Niag- 

 ara Group and T.gibbosa Hall, 1867 (Pal. N. Y., vol. iv, p. 272, pi. 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. 



