193 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 1 d. A specimen showing the corrugations more strongly. 
Fig. 1 e. An individual of full size in which the corrugations are well developed. 
Fig. If, g. Dorsal and ventral sides of an entire individual. 
Fig. 1 h. Profile view of the preceding specimen. 
Fig. 1 i. An old specimen where the corrugations are much stronger and closer than usual. 
Fig. 1 k, l, in. The interiors of several ventral valves, showing the area, crenulated hinge 
line, muscular and vascular impressions, etc. 
Fig. 1 n. Area of the ventral valve. 
Fig. 1 r. A portion of the area enlarged, showing the striated surface and crenulated margin. 
Fig. 1 s, t. Portions of the casts of the ventral valve of two different individuals, showing 
some slight difference in the character and strength of the impressions. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains; Schoharie, Carlisle, Catskill, Hudson, etc. 
The following species have no crenulations on the hinge line, and have 
broad triangular foramina, more or less closed by a pseudodeltidium, 
leaving the form of the foramen distinctly visible. 
Strophomena woolwoitliana (n. s.). 
Plate XVII. Fig. 1 & 2. 
Shell semielliptical, often extremely elongate. Ventral valve concave 
towards the front and flat on the lateral margins, depressed convex 
near the beak : beak small, and scarcely rising above the edge of the 
valve. Dorsal valve convex, most elevated near the front, and flattened 
towards the umbo : beak not projecting. Hinge line straight, equal to 
the greatest width of the shell. Area linear, conspicuous, partly common 
to both valves. Foramen broadly triangular, partially or entirely closed. 
Surface finely striated. Striae round, crowded, simple, increasing by 
interstitial addition, concentrically crossed by closely arranged striae 
and a few distant lines of growth. 
Ventral valve marked interiorly by a broad flabellate vascular area, 
which is partially limited by the dental lamellae : teeth strong, pro¬ 
jecting more or less into the interior of the valve ; in old shells, less 
conspicuous. Dorsal valve with vascular area strongly marked : cardi¬ 
nal process deeply bifid, and each division again trilobate upon the 
exterior side ; lateral lamellae curving as in Orthis. 
