74 NEW YORK STATE MUSEUM 



Horizon and locality. In the lower Bertie waterlime, 5 feet 

 above gypsum bed, at Sweet Quarry, Marcellus, N. Y., associated 

 with Eurypterus remipes and Lingula testatrix. 



Remarks. This small gastropod appears in densely crowded 

 flocks on the otherwise barren bedding planes of the waterlime. Tt 

 is similar to Hormotoma minuta Hall, a type from the 

 Manlius limestone of New York and the lower Monroe of Michi- 

 gan, but is somewhat larger, less ' slender and possesses more 

 rounded volutions. 



Pterinea poststriata nov. 



Plate 25, figures 5-7 



Description. Strongly inequivalve. The left valve highly con- 

 vex, the right depressed convex to nearly flat. Very inequilateral, 

 strongly oblique. Anterior height by one-half smaller than posterior 

 height. Beak about one-fourth of length of valve from anterior 

 extremity, prominent and projecting beyond hinge line in left valve, 

 depressed and not projecting beyond hinge line in right valve. 

 Cardinal margin straight and extending nearly the whole length of 

 the valve, anterior ear small, narrow, anterior extremity rounded. 

 Anterior margin slightly arcuate, curving obliquely to well-rounded 

 basal margin. Posterior margin very obliquely truncate, strongly 

 curved. Umbonal ridge high and distinct on left valve, its highest 

 part about one-third of its length from the beak, vanishing toward 

 the postero-basal margin. On the right valve only a low, broad 

 umbonal ridge extends halfway toward the postero-basal margin; 

 the rest of the valve is flat. Mesial sulcus undefined. Surface with 

 rather coarse growth-lines and concentric varices and fine 

 radiating lines on the posterior half, extending over the posterior 

 wing and to the crest of the umbonal ridge or a little beyond. 

 Anterior muscle impression about half the size of the posterior. 



Measurements. Largest specimen 33 mm long, posterior height 

 24+ (about 30 mm), anterior height 15.5 mm, thickness about 

 4 mm . Most specimens are smaller. A well-preserved right valve 

 measures 23 mm in length, 16 mm in posterior height, 11 mm in 

 anterior height. 



Horizon and locality. Pittsford shale at Pittsford, N. Y., in 

 both the shale and the waterlime bands where it occurs abundantly. 



This species has been compared by Sarle (Rep't N. Y. State Pal. 

 for 1902, p. 1085, 1903) with P. emacerata of the Rochester 

 shale but is stated by him to be a little more rhomboid and convex. 



