296 
Aug. F. Foerste 
29. Psiloconcha sinuata — borealis, var. nov. 
{Plate II, Figs. 9 A, B, C) 
Specimen about 22 mm. in length, with the hinge-line straight 
for a distance of about 7 mm. posterior to the beak, and then 
deflected downward for a distance of about 8 mm. at an angle of 
about 165 degrees with the hinge-line, before curving rapidly into 
the rather narrowly rounded posterior margin. Umbonal ridge 
and mesial sulcus very oblique, and only moderately distinct, but 
at least much more distinct than in most species of this genus. 
The umbonal ridge is most distinct within about 5 mm. of the 
beak, and below this part of the ridge the shell is distinctly flat- 
tened, the flattening becoming more concave on following the 
mesial sulcus toward the basal margin. The latter is compara- 
tively straight but in older specimens might easily become slightly 
concave. The chief difference between the form here figured and 
typical Psiloconcha sinuata, Ulrich, consists in the anterior outline, 
which is less quadrate, the hinge-line anterior to the beak being 
less in line with that posterior to the same, but rather deflected 
downward as in Psiloconcha inornata, Ulrich. Convexity of the 
single valve fully 2 mm. 
As the type of this form has been selected No. 8411 (plate II, 
Fig. 9B) from a group labelled as coming from the Riviere des 
Hurons and collected October, 1872, by Thomas Curry. Al- 
though no separate label was attached to this type specimen it 
is regarded as unquestionably coming from the same locality as 
the remainder. It is associated in the same slab with Clidophorus 
praevolutus Fig. 6, plate I. On plate II, Fig. 9A, represents the 
two opened valves of another specimen from the same locality; 
and bears the number 2087. Fig. 9C represents a similar speci- 
men collected by Aug. F. Foerste along the Nicolet River, south- 
west of Ste. Monique. It occurred somewhere beneath the 80-foot 
level below the lowest horizon containing Strophomena planum- 
hona, at the high river bluff south of the Lower Richmond expo- 
sures, and is numbered 8412. In my notes I called it Psiloconcha 
sinuata-minima . 
All of the specimens are preserved by the Geological Survey of 
Canada, in the Victoria Memorial Museum, at Ottawa. 
Psiloconcha inornata, Ulrich, is a distinctly flatter shell, with a 
scarcely ceptibleper umbonal ridge except in the immediate 
