STUDY OF THE GRAPTOLITES. 217 



Associated with the preceding forms, there are some stems of corneous 

 or carbonaceous texture, frequently branched, the branches again dividing, 

 and sometimes, if not always, in whorls ; in one of which six divisions 

 were counted. The general form of the body is not unlike that of De?i' 

 drograptus, but the branches are more slender, and ramify in a diflferent 

 manner, while there are no visible cellules. Without farther knowledge, 

 I refer these fossils, with hesitation, to the Glenus Oldhamia (O. fruticosa^ 

 Hall). 



The variety of form and mode of development among the graptolites is 

 shown, by the collections from the Quebec group, to be much greater 

 than had ever before been supposed. The number of species which have 

 been traced to their origin, or initial point, and whose mode of growth has 

 been verified, is probably larger than in all the collections heretofore made ; 

 and, together with those before known, enables us to give a very good expo- 

 sition of the characters of this family of fossils. 



SYNOPSIS OF THE GENERA OF GRAPTOLITID^. 



I. 



Species consisting of stipes or fronds, with a bilateral arrangement of the parts; 

 a solid axis, with a common canal extending along each series of cellules. 



1. The successive buds developed in tubular cellules, 

 which are usually in contact for a greater or le<?s 

 proportion of their length, and inclined towards the 

 axis. 



a. Cellules in single series along one side of al Graptolithus, LinncEus. 



Tj • Ci- + ^ I Sub-genera Monoprion,* 



common solid axis. Stipes, two or more, from ! r>j * nr 



^ ^ ' f> Diaymograptus, Mono- 



a common origin, with or without a central i graptiis, Tetragraptus, 



disc. j Dichograptus, etc. 



b. Cellules on one side of slender branches, which ^ 

 are developed on one or two sides of a long 



slender axis or rachis, the free extremities of } Ccenograptus, Hall, 

 which are likewise celluliferous. Ex. G. graci- i 

 lis and G. diver gens. ) 



c. Cellules developed in parallel arrangement on 1 



two sides of a common soMd axis. Stipes narrow \ Diplograptus, M'Coy. 

 elongate. Sub-genus Diprion. j 



d. Cellules developed in a cruciform arrangement 1 



on the four sides of a common or coalescent |- Phtllograptds, Hall. 

 axis. Stipes elliptical or sub-elliptical. j 



2. Cell-apertures excavated in the margins of the 

 stipes, without the tubular extension or calycle; 

 margins of cellules plain or ornamented. 



a. Cell-apertures upon the two sides of an elongate j 

 sublinear stipe. Graptolithus bicornis and } Climacograptus, Hall. 

 others. J 



* Should it be proved that there exist simple stipes with a single range of cellules, the 

 definition of this section will require to be modified, or a new sub-section made to include 

 such forms. 



[Assem. No. 239.] 28 



