DEVONIAN FAUNAS. dal 
twisted; cardinal area high, flat, slightly concave or convex; del- 
thyrium narrowly triangular, closed below by deltidial plates. Brachial 
valve depressed-convex, flattened toward the cardinal angles; mesial 
fold sharply defined, low, flattened on top with a slight, longitudinal 
mesial depression. Surface of each valve marked by from five to nine 
simple, subangular, radiating plications on each side of the fold and 
sinus, by finer concentric strizw and a few stronger lines of growth. 
The dimensions of a nearly-perfect, but rather small, specimen are: 
length, 9 mm.; width, 15 mm.; thickness, 11 mm. The approximate 
dimensions of a larger brachial valve are: length, 13 mm.; width, 
30 mm. 
Remarks.—Fragmentary specimens of this species are common in 
the fauna of the “trilobite bed,” but complete shells are rare. The 
species differs from C. varia Clarke of the higher beds in being larger 
and coarser in its general characters, in the more twisted or distorted 
beak of the pedicle valve and in the more nearly-flat cardinal area. 
MERISTELLA PRINCEPS Hall. 
Plate XLII., Figs. 27-28. 
1858. Merista princeps Hall, Pal. N. Y., vol. III., p. 251, pl. 44, 
figs. 1-5. 
Description.—Shell large, subovate in outline; the postero-lateral 
margins converging toward the beak in an angle of about 60°. Pedicle 
valve convex, the greatest convexity posterior to the middle; the lateral 
slopes curving rather sharply to the cardinal margins, depressed me- 
dially in the anterior half of the valve in a deep and more or less 
subangular sinus; beak prominent, incurved. Brachial valve strongly 
convex, much elevated along the median line towards the front; the 
lateral slopes curving rather strongly to the margins: Surface nearly 
smooth or marked by obscure, radiating and concentric striz, with a 
few more conspicuous lines of growth most prominent towards the 
margin. 
The dimensions of a large brachial valve are: length, 36 mm.; 
width, 35 mm.; convexity, 14 mm. 
Remarks.—This species is rarely represented in the “trilobite bed” 
in the Nearpass section, but is a little more common farther south. 
