266 PALEOZOIC PALEONTOLOGY. 
broadly rounded, ventral margin convex, anterior margin more sharply 
rounded than the posterior. Eye tubercle distinct, situated at about 
the centre of the antero-dorsal quarter of the valve. Anterior margin 
slightly flattened at the dorsal angle, the flattened area sometimes ex- 
tended for a short distance as a marginal border. Surface of the 
valves smooth. 
The dimensions of an average specimen are: length, 7 mm.; height, 
4.5 mm.; convexity of one valve, 2 mm. 
Remarks.—This species occurs abundantly in the Manlius limestone, 
where it is one of the most characteristic species. 
BEYRICHIA KUMMELI 2. sp. 
Plate XXIV., Fig. 21. 
Description.—Carapace subelliptical in outline, a little narrower in 
front, hinge-line straight, about three-fifths of the total length. Free 
margin with a depressed, concave border, whose outer edge is slightly 
elevated in a rounded, marginal ridge, outside of which the surface 
drops abruptly to the edge of the valve. Valve divided into three lobes 
by two furrows, which extend ventrally downward from the hinge-line 
to about the middle of the valve; the anterior furrow a, little shorter 
than the other, with its lower extremity slightly curved backward. 
Posterior lobe the largest, including nearly one-half of the valve, with 
a small, but distinct, tubercle a little in front of its middle point. 
Middle lobe subglobular in form, more highly convex than either of 
the others, with a shght, concave excavation at its base. Anterior 
lobe more depressed-convex than either of the others. Surface finely 
pitted, except on the marginal border and in the furrows; the pits 
appearing to be angular depressions, with narrow, dividing ridges. 
The dimensions of the type specimen are: length, 4 mm.; height, 
2.5 mm. 
BEYRICHIA WALLPACKENSIS 0. sp. 
Plate XXIV., Fig. 22. 
Description.—Carapace oblique, narrower behind, with a straight 
hinge-line, nearly equaling the total length of the valve. Posterior 
margin straight above, meeting the hinge-line in a little less than a 
