SILURIAN FAUNAS. 205 
tuberance is partially separated from the anterior lobe in front and 
the posterior lobe behind by a slight depression in the surface of the 
valve, which is continuous with the oblique portion of the anterior 
furrow. Surface of valves, except in the furrows and on the mar- 
ginal border, minutely pustulose. 
The dimensions of the type specimen are: length, 3.1 mm.; height, 
2.2 mm. 
BEYRICHIA JERSEYENSIS Nl. sp. 
Plate XXIII., Wig. 5. 
Description.—Carapace subelliptical in outline, height in front and 
behind nearly equal. Hinge-line straight, about two-thirds the length 
of the valve.. Free margin with a narrow, marginal border, which is 
flattened above and drops vertically to the edge of the valve externally. 
Valve divided near the middle by a narrow furrow, starting from the 
hinge-line and extending to below the middle of the valve, with a 
slight, forward curve. A second furrow originates from the median 
furrow a little below the hinge-hne and, after describing nearly a semi- 
circle towards the front of the valve, again joins the median furrow 
a little above the middle of the valve. The lower half of this semi- 
circular furrow is less deeply impressed than the upper, and a faint 
depression joins its upper portion with the dorsal margin of the valve. 
Surface of the valve smooth, regularly convex throughout, with the 
median, semi-circular lobe slightly more prominent. 
The dimensions of the type specimen are: length, 2.5 mm.; height, 
1.5 mm. 
BEYRICHIA NEARPASSI Nl. Sp. 
Plate XXIII., Wigs. 7-8. 
Description.—Carapace subelliptical in outline, the posterior ex- 
tremity equaling or a little narrower than the anterior; the hinge- 
line straight, about four-fifths of the total length of the valves. Free 
margin, with a flattened, marginal border. Valves divided into three 
lobes by two rather-broad and deeply-impressed, nearly-equal fur- 
rows, which start from the dorsal margin and extend vertically down- 
ward to about the middle of the valve. A shallower and less sharply- 
