GRAPTOLITES OF NEW YORK, PART 1 475 



for which hitherto indefinite terms as " radicle," " radicular bar " and " axillary 

 spine " had been used. He also recognized the formation of a solid axis in its 

 wall, a fact verified later on by Wii/ian, emphasized its importance for 

 specific distinction and defined the " angle of divergence," and arranged the 

 genera into families, which were brought under the subdivisions erected 

 before by HopMnson. This system will be further noticed in a later chapter 

 [p.544]. 



Rervmann [1885] monographed the family Dichograptidae and Jacket 

 [1889] published observations on graptolites obtained from diluvial boulders, 

 demonstrating the presence of an important difference in the thecal structure 

 of the species of Monograptus. 



AVhile the faunas of various regions had been thoroughly described 

 and a great number and variety of forms made known ; the succession 

 of the faunas and faunules had been established and an elaborate system of 

 zones obtained in several countries and these zones had been parallelized, 

 thus demonstrating a wonderful rapidity in the development of the graptolite 

 genera and their distribution over vast areas, still the problems of the internal 

 structure remained as unsolved as they had been left by Barrande and Hall. 

 This can not be wondered at, as the flattened carbonized specimens which 

 constitute nearly all collections are unfit for an elucidation of the internal 

 characters. 



It is true that a few keen observers drew some correct conclusions from 

 such material; but, as these were not readily verified, they did not find 

 general acceptance. Thus it was claimed by Scharenherg that the Diprion- 

 idae are in fact Monoprionidae, produced by an alternate gemmation of 

 thecae ; and Lapworth expressed his belief, when describing two species of 

 Dimorphograptus [1876], that there are no diprionidian forms, and the 

 sicula in all graptolites produces but one bud. These views of Scharenberg 

 and Lapworth, gleaned from shale material, have been found to be coi-rect by 

 recent investigations on specimens etched out of limestone. Positive evidence 

 was however not obtained till the preparation of sections of graptolites was 

 begun. 



