an PALEONTOLOGY 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. alia, but which, under a lens, show the pajjillose mai-kings. 



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 Pentamerns 

 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. RupEKT 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. 



Fig. 6 6. The same enlarged two diameters. 



Fig. 6 f. 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 orenula- 

 tions of the dorsal line, and the groove in the ventral niar"in. 



Geological position and locality. In the tentaculite limestone : Albany, Schoharie, 

 Greene, Herkimer, Oneida and Cayuga counties, in numerous localities. 



• Anuiil.; aiiJ Maguziiic of Natnrat History, Second scries, Vol. xvii, No. 98, p. 88. 



