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PALEONTOLOGY OF NEW-YORK. 
Genesee slate, and occurring generally in the more shaly portions of the 
Chemung group. 
Leiorhynchus limitaris. 
PLATE LYI. 
Orthis limitaris : Vanuxem, Geol. Report Third District New-York, p. 146, f. 3. 1842. 
Atrypa limitaris : Hale, Geol. Report Fourth District New-Tork, p.182, f. 11. 1843. 
Leiorhynchus limitaris : Hall, Thirteenth Report on the State Cabinet, p. 85. 1860. 
Shell ovate, suborbicular or transverse, moderately or extremely gib¬ 
bous, with the sinus and mesial fold more or less developed. 
Ventral valve in young shells scarcely less convex than the opposite, 
becoming gradually more dissimilar with the growth. In old shells 
the ventral valve is rather gibbous near the beak, and gradually 
depressed below, becoming deeply sinuate, produced in front and 
abruptly truncate; beak closely incurved. 
Dorsal valve more convex than the opposite, gibbous in older shells, 
the mesial fold becoming developed below the middle of its length; 
umbo gibbous, and often rising nearly as high as the beak of the ven¬ 
tral valve. 
Surface marked by numerous angular or subangular plications, those of 
the mesial fold and sinus distinctly bifurcating, while sometimes a few 
’ of those on the sides are divided ; concentrically marked by fine striae 
as in all the species of this genus. 
In the youngest specimens observed, the ventral valve below the 
umbo is flat or concave; while in those a little older, the two valves are 
nearly equal, and the shell is nearly circular. The illustrations oh Plate 
lvi present the principal varieties of form of this species. 
Geological formation and localities. This species is abundant in the Goniatite 
limestone of the Marcellus shale ; and in the absence of this limestone, it is 
abundant in certain layers of the Marcellus shale, always characterizing that hori¬ 
zon, a fact -which induced Mr. Vanuxem to give it the name limitaris. It is 
widely distributed, occurring in the Goniatite limestone in Schoharie, and in the 
same position at intermediate points as far as Marcellus in Onondaga county. It 
is abundant in the shale at Avon, at Leroy, near Alden, and at numerous other 
places within the State of New-York. I have not seen specimens from any western 
locality. 
