295 



Knightii,' 'which was gathered by Dr. Bigsby 'in 1823 ' on the Lake of 

 the Woods and presented by him to the British Museum,* as specimens 

 of the shell which I here call P. deeussatus have since been collected from 

 boulders on the south west shores of that lake by Dr. G. M. Dawson in 

 1873 and by Dr. A. C. Lawson in 1884. Other localities at which the 

 species has been obtained from boulders are as follows : — Nelson River, 

 about sixty miles above its mouth, Dr. R. Bell, 1879 ; Lower Fort Garry, 

 Dr. R. Bell, 1880 ; Kenogami River, s-ix miles above the mouth of the 

 Bagutchewan, Dr. R. Bell, 1886. Mouth of the Fairford River and Steep 

 Rock Island, Lake Manitoba, J. F. Whiteaves, 1888. North east side 

 of Lake Winnipegosis and Red Deer River near its mouth, J. B. Tyrrell, 

 1889 ; Virden, Manitoba, C. N. Bell, 1889. 



"In Appendix No. 1 to Franklin's ' Narrative of a Second Expedition 

 to the Shores of the Polar Sea, in the years 1825, 1826 and 1827,' " Sir 

 John Richardson says that ' Mr. Sowerby determined a shell, occurring 



in great abundance in the strata at Cumberland House ' . . ' to 



be the Pentamerus Aylesfordii,' which is regarded by Dr. Davidson as a 

 synonym of P. Knightii. Although Cumberland House is 135 miles far- 

 ther up the Saskatchewan than the locality at which Mr. Tyrrell obtained 

 P. deeussatus in place, it is by no means improbable that the specimens 

 which Mr. Sowerby determined as P. Knightii are really referable to the 

 present species. However this may be, it seems to the writer that P. 

 deeussatus differs materially from the true P. Knightii, especially in the 

 following particulars. The umbo of the ventral valve of the former is 

 narrower and less prominent, while its beak is much less strongly curved; 

 the coarser surface markings of both valves do not consist of com- 

 paratively distant and irregular radiating ribs, as in P. Knightii, but of 

 close set, irregularly disposed, unequal and not much elevated radiating 

 raised lines ; and the mesial septa of both valves of P. deeussatus are not 

 more than half the comparative length of those of P. Knightii." 



The fossil brachiopoda from the Saskatchewan River that were doubt- 

 fully and provisionally referred to Bhynchonella altiplicata, Atrypa reti- 

 cularis, and Trematospira formosa, in Mr. Tyrrell's Report, are too im- 

 perfect to be satisfactorily determined. 



MOLLUSCA. 



Pelecypoda. 



Pterinea occidentalis, Whiteaves. 



Saskatchewan River, at Grand Rapids below Old Portage, J. B. Tyrrell, 



1890 : the specimens referred to on page 287 ante, in connection with 



the original description of this species, which is figured on Plate 28. 



*Journal of a Boat Voyage through Rupert's Land and the Arctic Sea, vol. I, foot note 

 to page 62 ; and vol. II, p. 197. 



