STUDY OF THE GRAF TO LITE S. 



257 



The preeminence of the Quebec group, as the period of the greatest 

 development in the Graptolitidse, is shown in the above table. Of the 

 seventeen genera and sub-genera here enumerated, eleven are known in 

 this period; while four genera, viz: Phyllograptus, Dendrograptus, 

 Callograpttjs, and Ptilograptus, are not at present known in any higher 

 position than the Quebec group, though one of them occurs in the Pots- 

 dam sandstone. All those genera having the nearest relations with 

 GraptoUthus proper in the structure of their parts occur in this group, and 

 the species monoprionidion found in it are more numerous than in all the 

 subsequent formations, so far as at present known. 



In addition to circumstances originally favorable to their development 

 and growth, the subsequent condition presented during the period of the 

 accumulation of the materials of the Quebec group, in Canada, seem to 

 have been equally favorable to the preservation of graptolites, and in no 

 other formation have they been found with all their parts so entire. 



GEOLOGICAL DISTRIBUTION OF THE SPECIES OF GRAPTOLITIDJl IN CANADA AND 



THE UNITED STATES. 



* For subdivisions under this head see pp. 251 and 260. 



t All the species in this Table same author, unless otherwise indicated. 



\ Utica slate. 



Cab. Nat. 33 



GENERA AND SPECIES. 



i 



o 



d 



3 

 G? 



w 

 3 

 o 



=2 ^ 



o 



'a 



> 



c 

 o 



-a 



3 





i 



3 



2 



B 

 O 

 C 

 O 



1 



1 



o 



CD 



1 

 W 



S 



'a 



n 



3 



a 



o 



m 



3 

 o 



eg 



'a 

 o 



-s 



O 



Genus Graptolithus* 

 (Sub-genus Monoprion'), 



G. abnormis, HALLf 



alatus 





* 

 * 

 * 

 * 

 * 

 * 



* 



* 



* 



* 



* 



* 





* 

 * 

 « 





* 

























T-jio-sbvi 









clintonensis 



constrictus 



crucifer « 





denticulatus 



divergens 



evtensus 









flaccidusj 





fructicosus 





gracilis 



headi 





.. .. 



