Genus Graptolithus. 165 



gins of the branches are curved for a short distance from the ra- 

 dicle, and thence proceed in a uniform divergent line. The 

 entire branch is very narrow at the base, but becomes gradually 

 wider, the full width being attained at about half an inch from 

 the bifurcation, while a few of the serratures towards the outer 

 extremity, not having attained their full development, leave the 

 branches narrower in that part. The same feature is observed in ; 

 G. nitidus and others of this general character, and probably may 

 be observed in all species where the extremities of the branches 

 are entire. 



Locality and Formation. — Point Levy ; Hudson River Group. 



Collectors. — J, Richardson, E. Billings. 



Graptolithus patulus. 



Description. — Frond composed of two simple widely diverging 

 branches from a small radicle ; branches long-linear, having a 

 width from the base of the serratures to the back of the branch of 

 from one-sixteenth to one-twelfth of an inch ; serratures oblique, with 

 vertical mucronate points, which from base to apex are more 

 than half as wide as the branch. A well-defined line or ridge 

 extends downwards from the apex of the denticle two-thirds across 

 the branch. 



Fragments of this species are numerous upon some slabs of 

 greenish or blackish-green slate where no other species occurs. 

 The fragments are sometimes five or six inches in length, offering in 

 different individuals little variation in width. Sometimes the 

 branches are compressed vertically, and present the smooth, linear 

 base or exterior, which is less in width than when compressed 

 laterally. 



The lateral faces of the branches exhibit considerable variety 

 of surface, dependant on the degree of compression, or in some 

 instances, the replacement or filling of the interior by iron py- 

 rites. In such cases, or when the branch is not flattened, the sur- 

 face is deeply striated, or wrinkled obliquely. In some of the 

 extremely compressed individuals the surface has some appear- 

 ance of vesicular structure ; but this is probably due to influences 

 attending the mineralization of the fossil, or the filling up of the 

 original canal, and not to the structure of the substance itself. 



Locality and Formation. — Point Levy, Hudson River Group- 



Collectors. — J. Richardson, E. Billings. 



