TEENTON LIMESTONE. Ill 



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 Trenton limestone. It also reappears in the Hudson-river group, being 

 in some localities very abundant. 



147. 10. LEPTiENA FILITEXTA ( n. sp.) . 



Pl. XXII. 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 striae, 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 striae, which are crossed by fine elevated lines, giving the surface 

 a textile or woven appearance, which is remarkably characteristic in well preserved 

 specimens, and diflfers from any other species in this rock. 



Fig. 3 a. Ventral valve of a specimen of large size. The equal rugose striae are very distinctly preserved, 

 and also a few jubimbricating lines of growth near the margin. 



•Fig. 3 b. View of the cardinal area, showing the deflection at the extremities, and the convexity of the 

 shell. 



Fig. 3 e. 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 / An enlarged portion of the surface, showing the textile character. 



Positum 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. '*'"'« Collection.) 



