DEVONIAN FAUNAS. 311 
EATONIA SINGULARIS ( Van.). 
Plate XXXVL., Figs. 24-27. 
1859. atonia singularis Hall, Pal. N. Y., vol. III., p. 243, pl. 38, 
figs. 14-20. 
Description.—Shell broader than long, varying from broadly sub- 
ovate to subrhomboidal in outline, the postero-lateral margins meet- 
ing at the beak in an angle greater than 90°. Pedicle valve depressed- 
convex on the umbo, flattened or concave toward the lateral margins, 
depressed toward the front in a deep mesial sinus, which is produced 
in front in a lingual extension at nearly right angles to the plane of the 
valve; beak small, closely incurved over that of the opposite valve. 
Brachial valve strongly convex, with a conspicuous mesial fold toward 
the front; greatest elevation at the middle of the anterior margin. Sur- 
face marked by fine, radiating striz, which, on well-preserved speci- 
mens, are crossed by much finer, concentric strie. Usually a rather 
broad, flat, rounded ridge occupies the median line of the pedicle 
valve. Toward the front margin of full-grown shells there are several 
strong, closely-crowded, concentric lines of growth. 
The dimensions of a nearly-perfect, full-grown individual are: 
length, 16 mm.; breadth, 17.5 mm.; thickness, 12.5 mm. 
CENTRONELLA ? SUBRHOMBOIDEA DN. sp. 
Plate XXXVII.. Figs. 7-10. 
Description.—Shell subrhomboidal in outline, longer than wide. 
Pedicle valve prominent along the median line, sloping away to the 
cardinal and lateral margins; the cardinal margins infolded and 
forming a sort of false cardinal area; beak sharply pointed and 
slightly incurved. Brachial valve depressed-convex, most prominent 
near the middle. Surface of both valves marked by fine, concentric 
lines of growth, which are slightly fasiculate at intervals. Shell 
substance apparently punctate. 
The dimensions of the nearly-perfect type specimen are: length, 11 
mm.; width, 9.5 mm.; thickness, 6 mm. 
