216 
PALAEONTOLOGY OF NEW YORK. 
Leptodesma Lysander. 
PLATE XXII, FIG. 22 ; and PLATE XC, FIG. 34. 
L'ptodtama Lysander, Hall. Pal. N. Y„ voL v, pt. 1. Plates and Explanations: PI. 22, fig. 22. Jan., 1883. 
Shell of medium size, sub-rhomboidal; body ovate, abruptly narrowing 
toward the front, oblique to the hinge-line at an angle of about 45°; length 
one-third greater than the height; ante-byssal margin oblique above, curv¬ 
ing into the marked sinus, regularly rounded along the base and posterior 
extremity. 
Left valve depressed-convex below, more convex above, and moderately 
gibbous on the umbo. Right valve unknown. 
Hinge-line straight, about equal to the greatest length of the valve. 
Beak sub-anterior, moderately prominent. Umbonal region but slightly 
gibbous, subtending an acute angle. 
Anterior end broad, obliquely truncate; extremity slightly extended and 
acute. Wing narrow-triangular, joining the body at the posterior extremity; 
margin concave, greatest concavity just above the middle, thence turning 
outward it is produced into a spiniform extension of the cardinal line. 
Test marked by fine concentric striae, with sharp lamellae at nearly regular 
intervals over the body and wing, becoming crowded and fasciculate on the 
anterior of the shell. 
Interior unknown. 
A specimen has a length of 35 mm., height 24 mm., and hinge-line 
33 mm. 
This species differs from L. Corydon in its shorter and broader form; the 
body is less oblique and more abruptly narrowed toward the anterior; the 
striae are less abruptly recurved along the posterior slope. 
Formation and localities. In shales of the Chemung group at Kelly’s creek 
and Mansfield, Tioga county, Pa. 
