200 
PALAEONTOLOGY OF NEW YORK. 
joining the body near the posterior end; extremity produced, acute, and 
probably extended into a short spine. 
Test marked by fine striae of growth which are irregularly fasciculate, 
producing a slight undulation of the surface. The striae are lamellose on 
the anterior side and regular on the wing. 
Interior unknown. 
The specimen described has a greatest length of about 40 mm., height 25 
mm., and hinge-line 35 mm. 
This form differs from L. umbonatum in the lesser convexity and greater width 
of the lower part of the body; less abrupt depression on the anterior side from 
the umbo; the posterior slope less elevated and defined below the middle, and 
a much larger ante-byssal portion of the shell. 
Formation and locality. In the upper part of the Chemung group, Napoli 
Centre, Cattaraugus county, N. Y. 
Leptodesma naviforme. 
PLATE XXXI, FIG. 15 ; AND PLATE XXIII, FIG. 1. 
Lepiodesma naviforme, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 22, fig. 15; 
pl. 23, fig. 1. Jan., 1883. 
Shell below the medium size, rhomboidal; body very oblique, short-ovate ; 
length more than one-third greater than the height; anterior extremity 
subtruncate ; margin curving to the broadly rounded base ; posterior margin 
slightly produced, gently curving forward, nearly vertical. 
Left valve convex below, very gibbous above the middle. Right valve 
depressed-convex below, gibbous above. 
Hinge-line straight, more than one-third greater than the height of the 
shell. 
Beaks obtuse, situated at the anterior fourth of the hinge-line, prominent, 
directed slightly forward. Umbonal region gibbous, sloping abruptly into 
the wing. 
