258 THE DEVONIAN FOSSILS OF CANADA WEST. 
width from nine to eighteen lines; length a little more than half the 
width. 
The dorsal valve is moderately and pretty uniformly convex, gently 
or not at all depressed towards the cardinal angles ; area, sub-linear, 
lying nearly in the plane of the lateral margins, not reaching the 
extremities of the hinge line; beak, small pointed, scarcely at all 
projecting over the area ; mesial fold, rounded, not prominent, extend- 
ing quite to the point of the beak ; usually a large space at the cardinal 
angles, and extending thence along the hinge line to the sides of the 
beak without ribs; the latter in general obscure, rounded, not much 
elevated, and becoming obsolete before reaching the hinge line. 
Ventral valve rather strongly convex in the upper half, the outline 
in a side view forming about one quarter of a sphere ; the beak small, 
pointed, and incurved over the area ; the latter shorter than the hinge 
line, sloping outwards at an angle of about 115° at its base with the 
plane of the lateral margins, above rather strongly incurved ; foramen 
broad, and with a sharp ridge on each side, not always preserved. 
The mesial sinus is rounded or sub-angular, and extends quite to the 
point of the beak; a smooth space at the cardinal extremities as in 
the dorsal valve. 
Surface of the perfect specimens beautifully ornamented with 
shallow rounded concentric furrows, from three to four in two lines, 
the ridges between the furrows having from five to eight small elon- 
gated tubercles in the width of one line. 
Locality and Formation.—Occurs in the Corniferous Limestone at 
Rama’s Farm, and at many places in the County of Haldimand. 
Also in the Hamilton Shales in the Township of Bosanquet. Good 
specimens rare. 
Collectors.—J. DeCew, EH. Billings, A. Murray. 
SPIRIFERA RARICOSTA.—(Conrad.) 
DeELTHYRIS RARICOSTA.—Conrad. Journal of the Academy of Natural 
Sciences of Philadelphia, Vol. VIII., p. 262. Pl. 14, fig. 18. 1839. 
DELTHYRIS UNDULATUS.—Vanuxem. Geology of the Third District 
of the State of New York, p. 132, fig. 3. 1842. 
Description.—Sub-quadrate, sub-semicircular or oval; hinge-line- 
equal to the greatest width ot the shell or a little less; dorsal valve 
with five, and ventral valve with six, large rounded or sub-angular ribs ; 
