GRAPTOLITES OF NEW YORK, TART 2 47 



of a conclusion, is identical with D . complanatu s. The latter grap- 



tolite characterizes in Britain and Scandinavia the zone above that of 



Pleurograptus linearis. Lapworth [1880, p. 298] describes this zone as 



follows : 



Zone of Dicellograptus complanatus, Lapworth — The strata that lie 

 between the zone of P. linearis, Carruthers, and the summit of the Ordo- 

 vician system form in south Scotland two very distinct zones, though few 

 Rhabdophora have yet been described from there. The lowest zone is that 

 of Dicellograptus complanatus, Lapworth which contains but few peculiar 

 forms in addition to its characteristic species. It is recognizable in the same 

 stratigraphical position and affording the same fossils at Moffat (Barren 

 Mudstones), at Girvan, in County Down, at Rostanga in Scania in the 

 lower part of the Trinucleus schist, and in Westrogothia. 



If our determination of this graptolite is correct, the beds in Indian 

 Territory containing it would properly be correlated with this European 

 zone. 



Diplograptus crassitestus is a species with peculiarly coarse 

 structure and reminds in its entire habit most strongly of D . t r i f i d u s 

 Gurley ? a form already occurring in the same region in Normanskill time. 



Climacograptus mississippiensis is distinctly a later 

 derivative of Climacograptus typicalis and points to the rela- 

 tionship of this zone to the preceding one. It is a close relative or vicari- 

 ous form of C . 1 a t u s [see under C. mississippiensis] which is 

 found in the highest Champlainic (Ordovicic) graptolite zone of Europe, 

 that of Dicellograptus anceps. 



A summary of the analysis of the graptolite zones of the upper part of 

 the Champlainic and their correlation with those of Europe is found in the 

 correlation table at the beginning of this chapter. 



