GRAPTOLITES OF NEW YORK, PART 2 



IO9 



The monotypic genus Pleurograptus is characterized by its compound 

 secondary branches which are disposed irregularly on the main stipes. Its 

 late appearance in the Champlainic rocks and the character of its main stipes 

 which gradually become wider in distal direction indicate that it also is more 

 probably a derivative of Leptograptus 

 than of Nemagraptus or the earlier 

 Sigmagraptus. 



In surveying the various species 

 of Dicellograptus and Dicranograp- 

 tus, one cannot help noticing the 

 similarities between certain species 

 of the two genera, which suggest a 

 condition similar to that observed in 

 the genera Dichograptus, Tetragrap- 

 tus and Didymograptus, through 

 which various phyletic lines have 

 been found to pass indicating the 

 polyphyletic nature of these large 

 groups. 



In one of our cases a species 

 appears to be directly transitional 

 between two species, one a Dicello- 

 graptus, the other a Dicranograptus 

 and thereby clearly to point out the 



,1 _r 1 1 r .1 1 ,. Fig. 48 Dicellograptus smithi nov. Sicular 



path 01 development or the latter portions of rhabdosomes. xs 



genus. On account of its importance for the phylogeny of the groups 



involved, we will state this interesting case more fully. 



There is here described a species as Dicellograptus smithi 

 [see ibid, and fig. 48], which is remarkable for the variability of its form. 

 On one end it hinges toD sextans with which it has also the dimen- 

 sions and form of thecae in common, on the other to Dicran. fur- 

 catus. Some specimens indeed would be hardly distinguishable from 

 the latter species, were it not for the fact that the spines extend to but a 



