50 
Formation and Locality . Lowville, Parkdale avenue 
Ottawa, some distance west of the rest of the Ottawa section. 
The specimens are in the private collection of Mr. J. E. 
Narraway, Ottawa, for whom the species is named. 
Strophomena canadensis n. sp. 
Plate III, figure 7 
Width of shell slightly greater than length, the greatest 
width being about the middle of the shell. The measurements 
of the best preserved valve are: length 13 mm.; width 17 mm.; 
width of hinge line 14 mm. 
The shell in its nepionic stages is comparatively flat; the 
complexity increases gradually with age until at maturity it has 
an evenly-rounded convex form slightly resupinate at the 
extremities of the cardinal edge. A shallow depression begins 
at the beak, broadens out over the umbonal region, and gradually 
becomes more shallow and almost disappears at the ventral 
margin. Striae fine, from 9 to 1 1 in 12 mm. towards the anterior 
margin, increasing by bifurcation and implantation, principally 
the latter. There is a general gradual increase in the number 
of striae with increased growth, but at two places there is a 
marked increase, almost entirely by implantation, one about 
half-way between the beak and the margin, and the other, and 
more marked one, about two-thirds of the distance from the beak. 
The added striae are fine and with the more mature ones produce 
an effect of alternating- coarse and fine radiations. The shell is 
crossed by fine growth lines, which towards the anterior margin 
almost become cr'enulations. The whole surface is finely 
punctuate. 
The interior is not shown except that a slight exfoliation at 
the apex of the beak of one of the specimens shows the extreme 
point of the plates bordering the dental sockets. 
The shell averages smaller than S. prisca Raymond, and the 
alternations of the stria differ. S . prisca has two or three finer 
ones between the stronger striae. S. canadensis generally alter- 
nates one large and one small. S. canadensis differs also in 
possessing the shallow but evident depression. 
