LINGULyE OP 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 some 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 spatulata : Geological Reports of the Third and Fourth Districts, N.Y., 1842 8t 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. 
