374 
PALAEONTOLOGY OF NEW-YORK. 
under an ordinary lens. The test shows a tendency to decompose 
in minute points or punctations, which, beginning sparsely over the 
surface, finally cover it entirely, even in unweathered specimens ; 
while other specimens, which have been long weathered, present only 
scattered puncta. 
When I described the species from the Coralline limestone, I had no specimen of 
Leperditia alta with well-preserved surfaces, and referred it with doubt to that 
species; but a comparison of the perfect test of the two species shows a well-marked 
difference. There are, moreover, in the same rock with the larger specimens of L. 
jonesi in the Coralline limestone, small specimens which are scarcely distinguishable 
from L. alta , but which, under a lens, show the papillose markings. 
This species is extremely abundant in the Tentaculite limestone, literally covering- 
some of the layers, in the planes of bedding, for many feet in extent, and more or 
less abundantly scattered through the entire formation to the base of the Pentamerus 
limestone, in which rock it is of rare occurrence. In its geographical distribution, 
it is known to extend everywhere in New-York where the Tentaculite limestone 
occurs, and is as abundant in Herkimer county on the south side of the Mohawk, 
as it is along the west side of the Hudson in the Helderberg mountains, Schoharie 
and Catskill. 
Mr. T. Rupert Jones, F.G.S., has described some specimens from the shores of 
Wellington channel, which he refers with doubt to this species*. The condition of 
his specimens resembles that of the greater part of our own; and while his fig. 7 a 
resembles ours in form, the fig. 6 a is proportionally broader than any specimens 
of L. alta observed in our rocks. 
Fig. 6 a. View showing the form of a specimen of ordinary size. 
Fi". 6 b. The same enlarged two diameters. 
Fig. 6 c. Profile view. 
Fig. 6 d. The left valve of the same. 
Fig. 6 e. The interior of the right valve. The larger figure surrounding it shows the crenula- 
tions of the dorsal line, and the groove in the ventral margin. 
Geological position and locality. In the tentaculiteTiinestone : Albany, Schoharie, 
Greene, Herkimer, Oneida and Cayuga counties, in numerous localities. 
Annals and Magazino of Natural History, Second series, Vol. xvii, No. 98, p. 88. 
