LAMEL LIBRANCHIA TA. 
159 
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 Conradi. 
PLATE XX, PIGS. 1, 2, 4; and PLATE LXXXV’III, PIGS. 1-4. 
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. 
' Valves 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 ah 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. 
