256 PALEOZOIC PALEONTOLOGY. 
defined furrow extends vertically upward from the ventral margin, 
directly beneath the anterior furrow from the dorsal margin, the two 
being indefinitely connected across the middle of the valve by a slight 
depression. The posterior lobe is strongly convex and is the largest 
of the three, occupying about one-half of the total length of the valve ; 
medial lobe subglobular, about as high as the posterior one; anterior 
lobe about the same width as the median one, but less strongly convex. 
Entire surface of the valves smooth. 
The dimensions of an average specimen are : length, 1.75 mm.; 
height, 1 mm. 
BEYRICHIA DECKERENSIS Nn. sp 
Plate Pexcr hie phic wali: 
Description—Carapace subelliptical, a little narrower in front, 
hinge-line straight, a little more than four-fifths the total length of 
the valve. Free margin depressed in a narrow border from the 
postero-dorsal angle around the posterior margin, ventrally and an- 
teriorly the body of the valve is slightly inflated so as to project 
beyond the marginal border, entirely hiding it in a direct view. Valves 
divided into three lobes, by two vertical furrows, extending downward 
from the dorsal margin; the posterior furrow is the strongest, and 
extends beyond the middle of the valve, being but slightly curved 
forward below; the anterior furrow is shorter, and its lower extremity 
curves backward. ‘The posterior lobe is strongly convex, and occupies. 
about one-half of the entire valve; the median lobe is subglobular, 
having about the same elevation as the posterior one; the anterior 
lobe is lower than either of the others, and slopes gently to the an- 
terior margin; in width, it about equals the median lobe. Surface 
of the valve, except in the furrows and on the marginal border, very 
finely pitted. 
The dimensions of the type specimen are: length, 2.75 mm.; height, 
1.5 mm. 
