LINGUL^ OF THE HAMILTON GROUP. 13 



within which is a distinct groove nearly parallel with the margin an d 

 reaching half the length of the shell : the centre is marked by a longi- 

 tudinal linear impression for more than half its length ; and the cast 

 of one specimen preserves the mark of a thin septum, which extends 

 from just beneath the beak three-fourths the length of the shell. 



One specimen is nearly an inch and a half long, and the other one inch and one- 

 eighth. The thickened border and thin median septum are distinguishing features. 



There are somfi peculiarities in these specimens, which lead me to suppose that 

 a full knowledge of their characters and interior structure may authorise their 

 separation from the ordinary forms of Lingula. 



Geological formation and locality. In the shales of the Hamilton group, Ludlow- 

 ville, Cayuga county; and in a sandstone near Fultonham, Schoharie county. 



Lingula spatulata. 



PLATE I. 

 Lingula tpatulata : Geological Reports of the Third and Fourth Districts, N.T., 1842 & 1843. 



Shell small, subspatulate or subelliptical, moderately convex, attenuate 

 towards the beak, the ventral valve being more acute ; greatest width 

 across the middle of the shell ; length (which is scarcely three-tenths 

 of an inch) about twice as great as the width. Surface marked by fine 

 concentric striae, and, in the exfoliated shell, by faint. radiating striae. 



This little shell, without any very conspicuous features, is usually recognized 

 without difficulty by its small spatulate form. It is frequently abundant in the Ge- 

 nesee slate, and, so far as known, is confined to that rock; though its associate, the 

 Discina lodensis, occurs in the black slaty layers in the Hamilton group below. 



Geological formation and locality. In the Genesee slate, near Lodi and Bigstream 

 Point on Seneca lake; and near Ogden's Ferry, on Cayuga lake. 



