STUDY OF THE GRAPTOLITES. 



177. 



Thus far wc trace these forms through what a])})ear to be very natural 

 stages in the progress of development of the parts, which arc all constructed 

 upon the same plan, presenting only natural, and we may almost say con- 

 sequent moJiucatiens. 



The character of stipes and cellules in all these is such that the sepa- 

 rated fragments would afford no means of indicating whether the part 

 belonged to two, four, or eight-stiped species, or to those with numerous 

 simple stipes, or with branching stipes, unless the fragment retained a 

 bifurcation. It is on this account that I have not adopted several praposed 

 designations for the grapLolites with a single series of cells, since our col- 

 lections are mostly in a fragmentary condition, which must render it 

 impracticable, with our present knowledge, to make the proper reference. 



A variety of form is exhibited in the division termed Deudrograptus, 

 in which we may conceive of the numerous stipes iiear the base becoming 

 conjoined into one strong stem, with the bifurcating branchlets spreading 

 above, and this stem probably fixed in the soil. We then have a represen- 

 tation of the tj'pical forms of this genus, as in the accompanying figure, 

 and as illustrated on Plate iv of this memoir. 



Fig. 9. Pig. 10. 



Dendrograptus flexuosus. 



Dendrograptus halliamts. 



In this species, as shown in the enlargements of the branchlets, we have 

 a form of cellule similar to that in observed fragments of the ordinary 

 species of graptolites. The cellules are very minute, and, from the 

 frequent ramifications, this would probably always be recognized as a 

 branching species. 



Some of the forms of Dendrograptus have slender spreading branches, 

 and less rigid stems than the typical species, but still retain the angular 

 cellules. From these we pass almost imperceptibl}^ to the slender spread- 

 ing forms which I have termed Callograptus, plate iv, in whicli there is, 

 apparently, some slight modification in the form of the cellule, and the 



[Assem. No. 239.] 



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