WHITEAVES.] DEVONIAN FOSSILS, MACKENZIE RIVER BASIN. 235 



while the feebly developed mesial fold in its ventral valve is biplicated 

 near the front, where the two loLls are divided bj- a short groove. On 

 each side of the mesial fold and sinus there are two or three very faint 

 and short marsj-inal plications. 



In Europe P. galeatus has long been recognized as a Devonian as 

 well as a Silurian fossil, but it does not seem to have been previously 

 recorded as occurring in the Devonian rocks of North Amei'ica. 



Stringocephalus BtjRTiNi, Defrance. 

 Plate 29, figs. 10, 10a, 11 and 11a. 



Stringocephalus Buriini, Defrance. 1827. Diet, des Sc. Nat., vol. LI, p. 102, et 



Atlas, pi. Ixxv, figs, 1, la. 

 I'erebratula porrecla, Sowerby. 1827. Miu. Conch., pi. 576, fig. 1. 

 Stringocephalus Buriini, Duvidson. 1865. Men. Brit. Devon. Bracli., p. 11 (which 



see for a complete list of synonyms of the species), pi. i, figs. 



18-22, and pi. ii, figs. 1-11. 



Mackenzie Eiver, at the " Eamparts," E. G. McConnell, 1888 : two 

 casts of the interior of the closed valves, both of which are figured. 



One of these (figs. 10, 10a) is of the normal shape and of moderate 

 convexity. Its dimensions ai-e : — length, not unite two inches and 

 three quarters ; breadth, a little over two inches and three quarters; 

 thickness through the closed valves, exclusive of the test, about one 

 inch and three quarters. The dorsal valve is somewhat more conve.x 

 than the ventral, the thickness through the closed valves is much less 

 than their breadth or height, and the umbo and beak of the ventral 

 are prominent and nearly straight. The other (figs. 11 and 11a) which 

 is somewhat distorted, represents an unusuallj^ globose form of the 

 species, with the umbo of the ventral valve depressed and its beak 

 closely ]-ecurved over that of the dorsal. The approximate dimensions 

 of this Bjjocimen are: — length, two inches and a half , breadth, not 

 quite as great ; thickness through the closed valves, exclusive of the 

 test, which is not preserved, two inches and a quarter. The test of 

 this specimen seems to have been thick, judging by portions of it that 

 are left in the matrix from which the cast figured was broken. 



Cryptonella Calvini (?) Hall and Whitfield. 



Cryptondla Qdnni, Hall and Whitfield. 1870. Twenty-third Rei;-. Rep. N. Y. 

 St. Cab. Nat. Hist., p. 239. 



Mackenzie Eiver, at the " Eamparts," E. (J. McConnell, 1888, a few 



