LOWER HELDERBERG ROCKS. 
SSI 
Avicula sufoeqiiilatera (n. s.). 
Plate XLIX A. Fig. 6. 
Shell semielliptical, wider than long; hinge-line less than the greatest 
width of the shell below, depressed-convex in the middle ; umbones 
appressed ; base broadly rounded : anterior wing small, scarcely sepa¬ 
rated by a shallow sinus from the body of the shell; posterior wing 
large, separated from the body of the shell by a broad shallow sinus, 
from which the wing bends slightly outwards. 
Surface concentrically striated, without visible radiating striae. 
The shell is mostly exfoliated from the specimen, and its entire surface characters 
cannot be determined. 
Fig. 6. The left valve of this species. 
Geological position and locality. In the upper part of the pentamerus limestone 
of the Lower Helderberg group : Schoharie county. 
Avicula tennilainellata (n. s.). 
Plate LI. Fig. 1 & 2. 
Shell orbicularly subovate : left valve scarcely convex; right valve flat; 
hinge-line straight, shorter than the greatest width of the shell : 
anterior wing small, short, acute, separated from the body by a deep 
narrow sinus, not extending as far forward as the anterior ntargin of 
the shell; posterior wing short, broader than the anterior, acute at the 
extremity, not extending to the line of the posterior margin of the 
shell. 
Surface marked by a few unequal concentric wrinkles, and by fine, 
closely arranged, elevated, subimbricating, lamellose striae, which 
extend over the wings in like manner. Central portion of the shell 
marked by faint radiating striae. 
[ Paleontology III.] 36 
