No. 1.] DAWSON — POST-PLIOCENE. 19 



valve of Bithyrocaris? most beautifully sculptured, of which the 

 following is a description. The specimen is eleven lines in 

 breadth, and probably measured, when entire, nearly two inchcfe 

 in length. The dorsal border is rounded in a corresponding 

 degree with the ventral border ; a small rostrum is observable at 

 the anterior end, from which two prominent ridges also take their 

 rise and pass over the side, one arching towards the dorsal, the 

 other bending towards the ventral line, but uniting again on the 

 centre of the valve at one inch from the anterior end. The fine 

 striae above and below these prominent ridges are parallel, but ' 

 those inclosed in the central elliptical space cross one another so 

 as to form a finely reticulated pattern on its surface. The eye 

 spot is distinct and prominent at the anterior end, near the inter- 

 section of the two curved ridges. Other slight, scarcely visible, 

 folds traverse the carapace parallel to the ventral and dorsal 

 border, indicating that the original shell was of extreme tenuity, 

 like that of the recent Ajnis and Estheria. 



Should the discovery of other and more perfect specimens prove 

 this to be a true Dithyrocaris, it will be the first specimen of this 

 ccenus met with in rocks of Devonian aire. 



I had proposed to call this form D. striatus,^ but as there is 

 already a D. tenuisfriatus, it will be better not to give it so in- 

 distinct a name. I therefore beg to name it Dithyrocaris f Belli. 

 after its discoverer. 



THE POST-PLIOCENE GEOLOGY OF CANADA. 



By J. W. Dawson, LL.D., F.E.S., F.G.S. 



Introductori/ . 



When in 1855 the writer, in consequence of accepting the 

 office of Principal of McGill College, was removed from the 

 Carboniferous Districts of Nova Scotia, and thus to some extent 

 debarred from the prosecution of his researches in the carbonifer- 

 ous rocks of that Province and their fossil plants, he determined, 

 with the advice of Sir W. E. Logan, then Director of the Geo- 

 logical Survey of Canada, to take up as an occasional pursuit the 

 study of the Drift Deposits of Canada, a work which had, at 



♦ British Association Reports. Section C, Liverpool, 1870. 



