TRENTON LIMESTONE. 111 
Position and locality. The thin layers in the lower part of the Trenton limestone are often 
entirely covered with the perfect shells or separated valves of this species. In a higher 
position, it forms a large proportion of some thin beds, which, when split open, the surfaces 
present the pearly lustre of recent shells. In some western localities, as at Cincinnati and 
Oxford (Ohio), it is equally abundant, covering large surfaces of the strata. It occurs in 
all localities of the ‘T'renton limestone. It also reappears in the Hudson-river group, being 
in some localities very abundant. 
147. 10. LEPTNA FILITEXTA (n. sp.). 
Pu. XXXI. B. Figs. 3 a, b,c, d, e, f. 
Resupinate, broadly semioval ; hinge'line a little extended beyond the width of the shell, 
and deflected at the extremities ; dorsal valve concave, elevated towards the beak ; sides 
and front gently inflected ; ventral valve uniformly convex on the disc, regularly curving 
downwards towards the margin; surface marked by crowded equal striz, which are crossed 
by fine elevated concentric lines ; triangular foramen, in the concave valve, partially filled 
by the callosity of the opposite valve ; area moderately broad. 
This shell is characterized by its great proportional width upon the cardinal line, and its 
equal, regularly rounded strie#, which are crossed by fine elevated lines, giving the surface 
a textile or woven appearance, which is remarkably characteristic in well preserved 
specimens, and differs from any other species in this rock. 
Fig. 3 a. Ventral valve of a specimen of large size. The equal rugose striw are very distinctly preserved, 
and also a few subimbricating lines of growth near the margin. 
Fig. 3 6. View of the cardinal area, showing the deflection at the extremities, and the convexity of the 
shell. 
Fig. 3 c. Interior of the dorsal valve, showing the distinct and peculiar form of the visceral impression, 
and the partially closed foramen. The entire interior surface of the shell is papillose. 
Fig. 3 d. Dorsal valve of a smaller specimen, which is more abruptly inflected near the margin. 
Fig. 3 e. Cardinal view of the same, showing the deflection at the extremities of the shell, and the con- 
vexity of the ventral valve. 
Fig. 3 f. An enlarged portion of the surface, showing the textile character. 
Position and locality. This species is comparatively rare in the Trenton limestone, though 
several fine specimens have been found at Middleville, in the lower part of that rock. I 
have seen small specimens of the same species, from Mineral Point ( Wisconsin), and from 
Ohio, holding a similar geological position. (State Collection.) 
