158 PALEONTOLOGY OF NEW YORK. 



LEIOPTERIA, Hall. 

 Leiopteria l^vis. 



PLATE XVII, FIGS. 5-11 ; AND I'LATE XX, FIO. 5. 



^|jic((?a larvis. Hail. Geolog. Surv. N. Y. : Rei). Fourth Dist., p. 181. 1843. 

 Pleronltes lotvli, (Hall) S. A. Millek. Cat. Amor. Pal. Foss., p. 202. 1877. 

 Leiopteria Iwpis, Hall. Pal. N. Y., vdl. v, pt. 1. Plates and Explanations : PI. 17, figs. H-II. Jan., 1883. 



Shell small, .suh-rlioinboidal; body obliquely ovate; length and height nearly 

 ('f|ual ; greate.st length Ijelow the middle ; margins regularly rounded, some- 

 what extended on the post-basal side. 



Left valve more convex than the riglit ; the greatest convexit}" in both 

 valves is above the middle 



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

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



Beaks obtuse, rdimilci!. inclined forward, situated at the anterior third ol" 

 the shell, that of the lelt valve (|uite ]>rominent. Umbonal region ol' 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 ))y a distinct rounded sulcus 

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

 gnlar, tlat, limited by the post-umbonal slope; margin concave ; extremity 

 acute. 



Test tliin, iiiai-ked with distinct concentric stria? of growth, which are 

 crowded and conspicuous on the \viiigs. There are often oliscure traces of 

 radii, wliich are more distinct on tlie wing in casts or exfoliated specimens. 



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

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

 side of the umbo. 



One specimen has a length of II mm., heiglit 1 "J mm., hingc-linc about 

 10 mm. Another has a length of iU mm., heiglit I I mm., and liiugt'-line 12 



