68 NEW YORK STATE MUSEUM 



their biotic lines shows distinctly that the)' can not have been derived from 

 the Dicranograptidae, as formerly suggested, nor from any Leptograptidae 

 but that they probably go straight back to the Dichograptidae as indicated 

 by other morphologic considerations [see under phylogenetic notes]. 



Finally a small group of genera ( Monograptus, Cyrtolites) are our 

 faint indications of the third grand outburst of graptolitic types, that of 

 the Monograptidae in the Siluric. 



The synoptic table also brings out several facts of the zonal distribu- 

 tion of the genera which are otherwise not quite so apparent. The most 

 interesting of these is the generic composition of the third Deepkill zone, 

 which has in common with the preceding Beekmantown zones the Dicho- 

 graptidae, viz, Goniograptus, Loganograptus, Dichograptus, Tetragraptus, 

 Phyllograptus, Didymograptus and with the succeeding (Normanskill) zone 

 the Axonophora : Diplograptus, Glossograptus, Climacograptus, Crypto- 

 graptus, Retiograptus, while the second fauna of the Axonolipa, typically 

 represented by the family Leptograptidae, which appears in the Normans- 

 kill shale is here absent. It is mainly on account of the peculiar inter- 

 mingling of the disappearing genera of the first fauna of the Axonolipa 

 with the new appearing genera of the Axonophora that this zone has been 

 correlated with the Chazy formation. 



The Mesochamplainic, beginning with the zone of Nemagraptus 

 gracilis, is in the table seen to be characterized by the appearance of the 

 second fauna of the Axonolipa of the leptograptid and dicranograptid type, 

 with the genera Leptograptus, Syndyograptus, Pleurograptus, Amphigrap- 

 tus, Nemagraptus, Dicellograptus, Dicranograptus, and the continuance of 

 the Diplograptidae of the Chazy, as well as the appearance of the peculiar 

 genus Lasiograptus while of the first fauna, that of the Dichograptidae, 

 only Didymograptus is left. It survives, however, in various descendants as 

 set forth in another place. 



The table further brings out the interesting observation that, after the 

 Normanskill shale (zone of Nemagraptus gracilis), the Mesochamplainic is 

 unproductive of new genera, and still more so the Neochamplainic. I he old 



