Genus Graptolithus. 173 



Phyllograptus similis. 



Description. — Frond broad-oval ; margins ornamented by slend- 

 er, sub-mucronate serratures, -which are closely arranged, being in 

 the proportion of thirty-two to an inch, usually from thirteen to 

 sixteen upon each side ; axis disjoined ; radicle unknown. 



This species exhibits much variety of aspect. The more per- 

 fect forms are broadly oval, the diameters being about as six to 

 seven. The central portion is open and free from any organic 

 substance, as if there had originally been a cavity in the place of 

 the longitudinal axis. In other specimens the parts are separated 

 at one extremity, and appear like three or four branches closely 

 joined at the other extremity, giving it the aspect of a four-branch- 

 ed frond. On examining numerous specimens they appear to have 

 been originally arranged like the species of this genus already de- 

 scribed, with perhaps this difference, that the margins of the axial 

 portion were not closely united, or were quite disjoined along the 

 centre. From the equal extremities of the frond, and the almost 

 rectangular serratures, conjoinsd with the very obscure condition 

 of the specimens, it has not been possible to determine whether 

 the separation of the parts at the extremities has taken place at 

 the base or the summit. 



This species occurs associated with G. Logani and G. quad- 

 ribrachiatus. 



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



Collectors. — Sir W. E. Logan and James Hall. 



Besides the forms described in the preceding pages, there are 

 several others belouging to the genus Graptolithus, of which I 

 have not specimens in sufficient perfection to furnish a proper de- 

 scription ; and there are others which, possessing some abnormal 

 characters, I hesitate to describe as distinct species, until I shall 

 have an opportunity of seeing more specimens. One of these, 

 having the general character of G. octobrachatus, has but seven 

 bran chiefs, three from one extremity of the vinculum and four from 

 the outer, bifurcating as in the species named above. The 

 branches, however, are more slender than in G. octobrachiatus, 

 and it may prove to be a distinct species. 



Another form having the general habit of G. Logani has but 

 nine branchlets, four from one and five from the other side of the 

 vincolum. The exterior side only is visible, and the branches be- 

 ing broken off a short distance from the vinculum, no opportunity 



