348 
PALAEONTOLOGY OF NEW-YORK. 
sufficiently extensive collections to determine fully tliese characters, or whether it 
may be only another phase of that species in its young state. 
Geological position and locality. In the shaly and compact limestones of the Lower 
Helderberg group : Albany, Schoharie and Herkimer counties. 
Merista foella (n. s.). 
Plate XL. Fig. 1 a - p . 
Shell varying from suborbicular or subquadrilateral to transversely oval, 
usually somewhat broader than long, gibbous. Ventral valve a little the 
larger, most convex near the umbo : beak prominent and closely in¬ 
curved. Dorsal valve convex, gibbous in the middle and towards the 
umbo : both valves marked vvdtk a small sublinear mesial sinus, that 
of the ventral valve stronger than the other, the two often giving a 
distinct emarginate outline to the front. 
Surface smooth, or marked by faint concentric lines of growth, with 
much fainter indications of radiating striae. 
This species is characterized by its symmetrical form and the distinctly emargi¬ 
nate character of the front, caused by the meeting of the narrow mesial depressions 
of the two valves. The sinus on the front of the ventral valve is always broader and 
deeper than that on the other, giving a waved outline to the margins of the valves. 
Some of the specimens appear to have a small open foramen in the point of the 
beak, but which may be accidental. 
It is closely related to Terejbratula compressa ( Murchison), but attains a larger 
size than any of that species figured, and is almost always more gibbous, especially 
the ventral valve near the beak. 
A single specimen, perhaps of this species ( Plate xl, fig. 2 c, d, e &/'), is much 
more compressed than the others, and less distinctly sinuate on the middle of the 
valves, and consequently nearly destitute of the emargination in the front. I have 
regarded this one as a distinct species; but as no other specimens have come under 
my observation, I am inclined to consider it for the present as a variety of the M. 
bella. 
Fig. 1 a — h. Dorsal, ventral, profile, front, and cardinal views of young shells'. 
Fig. 1 i, lc, l. Yiews of a larger specimen. The species rarely attains a larger size than 
these figures. 
Fig. 1 m - p . Yiews of an unusually large specimen of this species. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains; Schoharie, Carlisle, and other places. 
