272 THE DEVONIAN FOSSILS OF CANADA WEST, 
RHYNCONELLA THALiA.—JW. Sp. 
Fig. 23. Fig.24. Fig. 25. 
Fig. 23, Rhynconella Thalia.—Dorsal view. Fig. 24.—Front view. Fig. 25.—Side view. 
Description.—Shell small, apical angle varying from about 70°, in 
very small specimens, to 105° in the large ones; sides straight in the 
upper half, regularly curved in the lower half; front broadly rounded 
with usually a portion in the middle straight, or even slightly con- 
eave’; valves about equally convex. Ventral valve with a sinus which 
gradually dies out at one half, or a little more, of the length from the 
front; beak acute, much elevated, slightly incurved; three simple 
acutely angular ribs in the mesial sinus, and six or seven on each side. 
Dorsal valve a little more strongly convex than the ventral valve; 
the front of the mesial fold elevated so that on the side view the base 
of the shell is a nearly straight line almost at a right angle with the lower 
part of the outline of the valve; umbo rounded with a faint mesial 
depression ; beak incurved into the cavity of the ventral valve; sur- 
face with four ribs on the fold, and six or seven on each side. 
Length of the largest specimen examined, four lines; width, four 
and one-fourth lines; depth, two and a half lines; width of the sinus, 
nearly two lines ; apical angle, 102°. 
Another specinen is four lines wide, three and a half in length, 
two in depth, sinus, two lines, and apical angle 105°. 
A third is two lines and three-fourths in length, and the same in 
breadth ; depth, one line and three-fourths ; apical angle, 88°. The 
sinus is distinct but not deep. 
Specimens less than two lines in length exhibit scarcely a trace of 
a sinus, and have the apex more acute than any of the above-men- 
tioned. 
This species closely resembles the ordinary Lower Silurian forms, 
such as R. plena, and young individuals of R. increbescens. 
Locality and formation.—Near Woodstock. Corniferous Lime- 
stone. 
Collector.—A. Murray. 
