New Species of Fossils. 297 



two mm. ; amount of recurvature of beak of ventral valve, 

 sixteen mm. 



The only locality at which this species is known to the 

 writer to have been certainly found in place, is in a light 

 brownish yellow dolomitic limestone at the foot of the 

 Grand Eapids of the Saskatchewan, where a number of fine 

 specimens were collected by Mr. Tyrrell in 1890. Boulders 

 containing it have been found at several localities in Mani- 

 toba and elsewhere in the central portion of the Dominion. 

 It is almost certainly the shell referred to by Sir John 

 Eichardson as a " Pentamerus, very like P. Knightii, 1 ' which 

 was gathered by Dr. Bigsby "in 1823" on the Lake of the 

 Woods and presented by him to the British Museum, 1 as 

 specimens of the shell which I here call P. decussatus 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 fol- 

 lows : — Nelson River, about sixty miles above its mouth, 

 Dr. E. Bell, 1879 ; Lower Fort Garry, Dr. E. Bell, 1880 ; 

 Kenogami Eiver, six miles above the mouth of the Bagut- 

 chewan, Dr. R. Bell, 1886. Mouth of the Fairford Eiver 

 and Steep Eock Island, Lake Manitoba, J. F. Whiteaves, 

 1888. North east side of Lake Winnipegosis and Eed 

 Deer Eiver near its mouth, J. B. Tyrrell, 1 889 ; 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 Eichardson 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 farther up the Saskatchewan than the locality 

 at which Mr. Tyrrell obtained P. decussatus in place, it is 

 by no means improbable that the specimens which Mr. 



1 Journal of a Boat Voyage through Rupert's Land and the Arctic Sea, vol. 1, 

 foot note to page 62. See also Ibo vol. ii, p. 197. 



