254 NEW YORK STATE MUSEUM 



Dimensions of the only observed example : length to byssal furrow, 



3 mm, hight 5 mm, length of byssal margin 5.5 mm, width of flange 1 mm. 



Habitat. Genesee province; Naples subprovince. Parrish gully, 



Naples. 



Pterochaenia elmensis sp. nov. 



Plate 4, fig. 26, 27 



Shells large for this genus, elongate, marginal curve suboval over the 

 pallial region, byssal margin very long, straight, almost attaining the full 

 hight of the valve. Posterior margin rather abruptly expanding from the 

 beak out. Byssal flanges narrow, separated from the body of the valve by 

 a sharp furrow, to which the slope from the body of the valve is abrupt. 



Surface smooth, only fine concentric lines being visible, with faint 

 radial lines sometimes apparent on the inner layers. 



Dimensions. Hight 11 mm, length 10 mm, length of byssal margin 

 10.5 mm. 



Observations. This species is the largest representative of the genus 

 observed, and, while approaching P. fragilis more closely than any 

 other, may readily be distinguished therefrom by its very long byssal 

 margin and narrow flanges. This margin however is shorter than in 

 P. perissa and the flanges narrower. 



Habitat. Genesee province ; Chautauqua subprovince. Big Buffalo 

 creek, East Elma, Erie co. 



Pterochaenia cashaquae sp. nov. 



Plate 4, fig. 20-25 



This is a very small shell, never even approximating the dimensions of 

 any other of the shells of this genus here described. It differs from P. 

 fragilis in having a long, straight oblique byssal margin, not halving 

 the valve as in P. perissa, but directed toward the antelateral extremity 

 at an angle of less than 45 with the axis of the shell. The antelateral 

 curve is much more broadly rounded than in either of the species men- 

 tioned. The byssal groove is quite broad and bears no ridge on its bottom; 

 the byssal flanges are narrow and extroverted. The body of the shell is 



