LINGULJE OF THE HAMILTON GROUP. 
7 
LINGUL2E OF THE HAMILTON GROUP, 
INCLUDING THE HARCELLUS SHALE. 
Lingula exilis. 
PLATE I. 
Lingula exilis : Hall, Thirteenth Report of. the Regents on the State Cabinet, 1860, p. 76, f. 2. 
Shell broad-ovate, moderately convex, length little greater than the 
width; apex obtuse ; cardinal margin obtusely rounded; sides regu¬ 
larly curving; base broadly rounded. Surface lamellose, with irregular 
rugae or lines of growth. 
The specimens obtained are imperfect at the beak, or in some other part. The 
shell is very broad ; and the great width at the apex, and broadly rounded cardi¬ 
nal extremity, distinguish it from all other forms of the Hamilton group, or of 
the rocks of New-York. In the normal condition, the umbo appears to have been 
quite prominent; but the specimens occurring in the thinly laminated strata are 
much flattened. 
It is associated with Discina and Conularia, similarly with those of the Tren¬ 
ton group in New-York. 
Geological formation and locality. In the Marcellus shale, near Bridgewater; 
and an imperfect specimen has been found in the shales of the central part of the 
Hamilton group, in Schoharie county, New-York. 
Lingula ligea. 
PLATE I. 
Lingula ligea : Hall, Thirteenth Report of the Regents on the State Cabinet, I860, p. 76. 
Shell narrow elliptical; length equal to twice the width; sides regu¬ 
larly curving; extremities subequal; margins of the valves thickened. 
Surface marked by fine concentric striae, and by a few obscure or obso¬ 
lete radiating striae. The more convex valve shows, along the inner 
margin, a narrow shallow groove as if the edge of the opposite valve 
closed just within its margin. 
