216 PALAEONTOLOGY OF NEW YORK. 



Leptodesn \ Lys lnder. 



PL \\Y. \\\l. FIG. 22; \m> P] \ II E< FIG U 

 I ptod ma Lysander, Hall. Pal. H ST., 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 binge-line at an angle of about 45°; Length 

 one-third greater than the beighl ; 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 h\ fine concentric stria?, with sharp lamella? at nearly regular 

 intervals over the body and wing, becoming crowded and fasciculate on the 

 anterior of the shell. 



Interior unknou n. 



A specimen has a length of 35 mm., height 24 mm., and hinge-line 

 33 linn. 



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 arc 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. 



