Genus Graptolithus. 147 



In some specimens the branches are broader and flattened near 

 the base, and the connecting bar or vinculum is broad and strong 

 with a small central node, the base of the radicle. Some portions 

 of the corneous membrane or disk are preserved in a single speci- 

 men. 



The subdivisions of each branch are from fifteen to twenty, or 

 perhaps more numerous when entire ; giving from sixty to eighty 

 or rfiore branchlets at the extremities of the frond. 



A distinguishing feature of the species is its rigid and divergent 

 bifurcation, and the almost uniform size of the branchlets. 



All the specimens of this species examined are in a coarse are- 

 naceous shale, and present the exterior or non-celluliferous side 

 only. A single specimen has the extremities of the branches 

 partially turned on one side, and gives some obscure indication of 

 serratures. Individuals are extremely numerous in certain layers 

 and are spread out in profusion upon the surfaces of the slate, the 

 bifurcating and interlocking branchlets presenting a net-work in 

 which it is extremely difficult to trace the ramifications of each 

 individual. 



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



Collectors. — J. Richardson and E. Billings. 



Graptolithus octobrachiatus. 



Description. — Frond composed of eight simple undivided branch- 

 lets, arranged bi-laterally, and proceeding from the two extre- 

 mities of a short strong vinculum, which is subdivided, and each 

 part again divided near the base, giving origin to four equal rays 

 or branchlets. Branchlets strong, linear, not sensibly diminishing 

 in size as they recede from the centre ; subangular, flattened upon 

 the outer side, with a depressed line along the centre ; obliquely 

 striated ; serratures short and strong, twenty in an inch, varying 

 in depth according to the position of the branch, in one or two 

 instances showing a deeper indentation. 



This species presents the essential characteristic of eight simple 

 arms or branchlets, which appear to have been subquadrangular 

 in its living state, and when compressed laterally are scarcely 

 broader, excepting the serratures, than when vertically compressed. 



The branches are formed by the division of the vinculum at 

 each extremity, first into two parts, making four ; each of these is 

 again subdivided almost immediately, and often so close as to 

 present the appearance as if the four branchlets on each side ori- 



