SPENCER NIAGARA FOSSILS. 561 



consisting of a radicle and a few branches. Tliat these are young- 

 specimens is apparent. But as the structure is not recognizable, 

 and the branching too rudimentary, it is impossible to determine 

 their place. In D. retiformis^ and some other species where 

 we find very great variations in size, the smaller specimens have 

 their structure and parts as fnlly developed as in the larger, and 

 the growth appears to have been only the lengthening of the 

 polyparies, without the lower portions becoming any stronger. 

 Classtfication of the Graptolites. 



The resemblance of the Niagara Graptolites to the more com- 

 plex forms of the Quebec g'oup is very striking. Our species of 

 Dictyonema are not distantly related. Especially are the forms 

 of Dendrograptus and Callograptus closely allied to those of 

 the older group. Again, Cyclograptiis is here the solitary repre- 

 sentative of the discoid types of the Cambrian period, and much 

 more beautiful. Some new forms appear, but these are nearly 

 allied to the older genera. 



In the classification of the Graptolites I have followed Prof. 

 Hall, which is here given, together with those newly discovered 

 forms belonging to the Niagara group. 



Synopsis of the Genera of Graptolitid^. 

 I. 

 " Species consisting of stipes or fronds, with a bilateral arrangement of 

 parts; a solid axis, with a common canal extending along each series 

 of cellules." 



1. "The successive buds developed in tubular 

 cellules, which are usual 

 greater or less proportioi 



f Graptolithus 



(a) Cellules on one side of solid axis. I ^^^^^ '"^^ ^"^' 

 ^ ^ ) genera) and 



1^ Ccenograptus. 



{b) Cellules on two sides of axis. j- Diplograptus. 



(c) Cellules on four sides of common ) 



axis. 5 Phyllograptus. 



2. "Cell-apertures excavated in margins of 

 the stipes, without tubular extension or 

 calycle; margins of cellules plain or orna- 

 mented." 



{a) " Cell-apertures on two sides of ^ 



sublinear stipe." ^ Climacograptus. 



developed in tubular •\ 

 ally in contact for a > 

 )n of their length." J 



