POTSDAM SANDSTONE. d 



Position and localities. This species is apparently confined to tlie Potsdam sandstone, 

 though usually uuassociatod willi any otluT Ibssil. It is found, though somewhat rarely, in 

 the valley of Lake Chaniplain ; and it also appears in the jjartially altered sandstone of 

 the same age, at the base of the Green Mountains, in Adams, Mass. Rolled masses of the 

 same rock, containing this fossil, are not unfrcquent in the eastern part of New- York. It 

 occurs in the same sandstone in several localities in New-Jersey. In the sandstone of the 

 same age on the Susquehanna, and at other places in Pennsylvania, this fossil is of frequent 

 occurrence ; and it may be traced in the same rock, through Maryland and Virginia, to 

 Tennessee. , {State Collection.) 



Lingula prima. Conrad. 



2. 1. LINGULA PRIMA. 



Pl. I. Figs. 2 a, b. 



Obtusely oval or rounded, short, obtuse at both ends ; sides curved ; base rounded ; beak 

 scarcely rising above the margin of the shell ; surface marked by faint concentric lines and 

 sometimes a few concentric wrinkles, and fine longitudinal stria-. In some specimi-ns, the 

 concentric and longitudinal striae are equally distinct, while in others the longitudinal strite 

 are more distinct. 



In its form and general aspect, this shell bears considerable resemblance to L. carta of 

 the Trenton limestone and Utica slate ; but that shell is usually larger, less obtuse at the 

 beak, with strong concentric stria;, while the longitudinal ones arc indistinct or obsolete. 



Position and localities. This fossil is for the most part rare even in the Potsdam sandstone, 

 though at Keeseville in Essex county it is quite abundant, forming distinct laminie in the 

 rock, like films of carbonaceous matter. It extends, according to Dr. Emmons {Geol. Rep. 

 p. 268), through a thickness of seventy feet of the rock at this place. It occurs also at 

 Rosse's biidge, four miles west .of Essex village, Essex county. (State Collection.) 



3. 2. LINGULA ANTIQUA* (n. sp.). 



Pl. I. Figs, 3 a, b, c, d, e. 



Elongated, subspatulate, rapidly tapering towards the beak ; sides usually straight, 

 sometimes abruptly curved ; front broadly rounded ; surface marked by concentric lines ; 

 no visible longitudinal striaa. 



* The figure given by Prof. Emmons {Geological Report, p. 2CS) as Lingula antiqua of the Potsdam sandstone, 

 is the L. acuminata (Conr.\d, Annual Report «/lS39, p. 64) of the Calciferous sandrock, and is not known to me 

 as a fossil of the Potsdam sandstone. The original specimen from which the figures were taken, in the collection of 

 Mr. Vajsuxem, bears a close resemblance to L. attemeata of Murchison's Silurian System, p. C41, pl. 22, fig. 13. 



1* 



