New and Little Known American Paleozoic Ostracoda. 115 
TETRADELLA SUBQUADRANS, Nn. Sp. OY Var. 


Fig. 2. TZetradella subquadrans, n. sp. or var. Trenton Group, Trenton 
Falls, N. Y.; a, left valve, x 20; 4, dorsal view of same; 
c, posterior view of same. 
Valves oppressed, slightly elongate, sub-quadrate, the dorsal 
edge straight, long, the posterior end vertical in the upper half, 
below bending rather sharply into the somewhat straightened or 
gently convex ventral margin. Anterior end oblique, rounding 
with a gentle uniform curve from the antero-dorsal angle to the 
emer of the ventral edge. A wide concave border or “ frill” 
around the free margins. The four ridges sharply defined, all 
connected, and seeming to spring from the postero-ventral region 
of the valve; the first or anterior ridge follows the curve of the 
ventral and anterior ends; the antero-median ridge, which is the 
most prominent portion of the valve, crosses it in a course nearly 
parallel with the first, terminating at the dorsal edge a little in 
front of the middle; the post-median ridge is short, directed 
only a little forward, and does not reach the dorsal margin 
the posterior ridge follows the posterior edge, thus completing the 
semi-circle begun by the anterior ridge. 
size: Length, including frill, 2.05 mm.; height, with same, 1.15 
mm.; without frill, length, 1.65 mm; height, 1.0 mm. 
This species is clearly distinct from all forms known from Amer- 
ican deposits, but may be only a variety of the English Bala 
species, Beyrichia complicata, Salter. The American specimens 
differ in being more nearly quadrate, and in having the post- 
median ridge longer and farther separated from the posterior ridge. 
In any event the two forms must be closely related. 
