I til PALAEONTOLOGY OF NEW YORK. 



Leiopteria Dekavi. 



PLATE XIX, FIG I ; PLATE XX, FIGS 16-18; AM) PLATE LXXX\ III. FIGS .V10 



Leiopteria Dtkayi, Hall. Pal. N. Y . vol. v, pt. 1. Plates and Explanations: PI. 19, fig. I : pL 20, figg. 



16 is. (in in error). .Ian., 1883. 



Shell of medium size, sub-rhomboidal in general form; body narrowly ovate, 

 oblique; length about equal to the height; anterior margin nearly vertical 

 for one-third the length of the shell, thence broadly rounded over the basal 

 margin and abruptly recurved at the post-basal extremity. 



Left valve convex, gibbous on the umbo. Right valve smaller and less 

 convex; the limitation of the wing not strongly defined. 



Hinge-line straight. Length a little less than the length of the shell 

 measured from the anterior side of the beak to the extremity of the wing. 



Beaks anterior, acute, prominent, inclined forward. Umbonal region 

 gibbous above, regularly convex below, subtending an acute angle. 



Ear 1 lending downward, with a strong fold in the upper part, limited by 

 a broad undefined sulcus and shallow byssal sinus. Wing triangular, fiat. 

 defined by the abrupt retral bending of the stria' and a depressed line along 

 the post-cardinal slope ; margin concave; extremity acute. 



Test thin, marked by fine regular concentric stria', which at unequal 

 intervals are crowded into fascicles, giving an undulated aspect to the surface 

 of the cast ; in old specimens, more crowded on the anterior side and ear. 

 and on the wing usually regular, sometimes becoming a little fasciculate on 

 the margin. 



This description of the surface is taken from casts or partial casts which 

 preserve more or less the surface markings. In a few younger specimens 

 from the shales, the surface shows line regular striae which gradually become 

 fasciculate as the shell increases in size. 



Ligamental area narrow, marked by fine stria' ; below this area is a narrow 

 oblique fold or lateral tooth. 



The three specimens figured on plate xx. have respectively the following 

 dimensions: Length '■'>'. 31, and 29 mm., heighl 37, •"•<*. and 30 mm., hinge- 



