L58 PALAEONTOLOGY OF NEW YORK. 



LEIOPTERIA, Hall. 

 Leiopteria l^vis. 



PLATE XVII, FIGS. S-ll ; AND PLATE XX, FIU. 5. 



Avieula lams, Hall. Geolog. Surv. N. V. : Rep. Fourth Dist., p. 181. 1843. 

 Ptmmites Icevis, (Hall) S. A. Miller. Cat. Amer. Pal. Foss.. p. 202. 1877. 

 Leiopteriu lOSttis, Hall. Pal. N. Y., vol. v, ]>t. 1. Plates and Explanations: PI. 17. tij;s. 5-11. Jan.. 1883. 



Shell small, sub-rhomboidal ; body obliquely ovate; length and height nearly 

 equal; greatest length below the middle; margins regularly rounded, some- 

 what extended on the post-basal side. 



Left valve more convex than the right; the greatest convexity in both 

 valves is above the middle. 



Hinge-line straight on the posterior side of the beak, turning abruptly 

 downward in front ; entire length greater than the length of the shell. 



Beaks obtuse, rounded, inclined forward, situated at the anterior third of 

 the shell, that of the left valve quite prominent. Umbonal region of left 

 valve prominent, subtending an acute angle. 



Ear triangular, nearly equilateral, with a strong angular fold along the 

 middle, separated from the body of the valve by a distinct rounded sulcus 

 and broad byssal sinus ; margin rounded ; extremity obtuse. Wing trian- 

 gular, Hat, limited by the post-umbonal slope ; margin concave ; extremity 

 acute. 



Test thin, marked with distinct concentric striae of growth, which are 

 crowded and conspicuous on the wings. There are often obscure traces of 

 radii, which are more distinct on the wing in casts or exfoliated specimens. 



Ligamental area narrow, with a single distinct groove. Some specimens 

 apparently indicate the existence of an oblique lateral tooth on the posterior 

 side of the umbo. 



One specimen has a length of 11 mm., height 12 mm., hinge-line about 

 Id mm. Another has a length of 10 mm., height 11 mm., and hinge-line 12 



