THE 



CANADIAN 



NATURALIST AND GEOLOGIST. 



Volume III. JUNE, 1858. Number 3 



ARTICLE XVI. — Note upon the Genus Graptolithus, and de- 

 scription of some remarkable new forms from the shales of 

 the Hudson River Group, discovered in the investigations of 

 the Geological Survey of Canada, under the direction of Sir 

 W. E. Logan, F.R.S. By James Hall. 



[Continued from our last.) 

 Graptolithus Headi. 



Description. — Frond robust, four-branched ; disk large, sub- 

 quadrangular, moderately extended along the branches ; branches 

 strong, much elongated, sub-angular exteriorly ; serratures small, 

 acute, from twenty-two to twenty-four in . an inch ; fine distinctly 

 marked strise extend from the base of the serratures nearly across 

 the branch. 



The specimen described presents the disk, which in its diame- 

 ter across the centre between the branches is nearly one inch and 

 an eighth, or nine-sixteenths of an inch on each side of the centre ; 

 while from the centre to its extent along the branches it varies 

 from about three-fourths of an inch in one branch to an inch in 

 another. The substance of the disk is strong and somewhat ru- 

 gose, either from its original character or from the accidents ac- 



