Lamellibranchiata. 335 



the valve by a distinct rounded sulcus and broad byssal sinus; 

 margin rounded ; extremity obtuse. Wing triangular, flat, 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 10 mm. Another has a length of 10 mm., height 11 mm., 

 and hinge-line 12 mm. A small specimen is 8 mm. in length, 9 

 mm. in height, and hinge-line 10 mm. 



Formation and localities. In the Marcellus shale at Littleville, 

 Livingston county, Alden, Erie county, and East Bloomfield, Ontario 

 county, N. Y. 



Leiopteria Oonradi. 



Leiopteria Conradi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations . 

 . PI. 20, figs. 1, 2, 4 (5 in error). Jan., 1883 



Shell above the medium size, sub-rhomboidal ; body oblique-ovate ; 

 length a little greater than the height; anterior margin straight, 

 nearly vertical ; basal and posterior margins regularly rounded. 

 Valvea sub-equally convex ; the left valve somewhat more convex 

 than the right. Hinge-line straight, longer than the length of the 

 valve, greatly extended posteriorly. Beaks acute, directed forward, 

 prominent, situated near the anterior end of the shell. Umbonal 

 region gibbous (in well-preserved shells), moderately convex below, 

 subtending an acute angle. Ear short, separated from the valve by 

 a rounded depression or sulcus, marked by a shallow, elongate byssal 

 sinus , extremity rounded. Wing triangular, much extended ; 

 margin concave; extremity acuminate. 



Test, as indicated by casts or partially exfoliated specimens, 

 marked by fine, closely arranged, concentric lines of growth, which 

 at irregular intervals are crowded and raised into rounded or sub- 

 angular fascicles, giving the surface a decidedly undulated aspect. 

 The striae become more crowded upon the cardinal expansions, 

 especially upon the ear. Ligamental area marked by a single 

 longitudinal groove parallel to the hinge-line. 



Two specimens of the left valve have respectively the following 

 dimensions: length 39 and 42 mm., height 32 and 36 mm., hinge- 

 line 42 and 47 mm. 



