ro4 



XKW YOItK STATE MrSET'M 



with their dorsal sides, but he considered the structure as analogous with that 

 of Diplograptus, assuming that the fi'onds of the latter wei'e formed by the 

 coalescence of two raonoprionidian branches, and as a corollary he infei'i-ed the 

 ■presence of a solid axis oi- virgula as in Diplograptus. The ]'luil)dosomes of 



Fi)f- 9i PhyDogvaiitus anitustifolius Hall, o View of a rliaBdosomc. etched out of 

 limestone. Seen iiom the leverse lanti.aiculai) side. .\4 J) Sieiilar end of rhubdosonie, seen from 

 the obverse (sicular) side. .\0 c Khabdosome seen from the sicular end. Shows the apertures of 

 the sicula (in the center), of the Hrst two theoae (tlankinx the sioula), and of the earliest portions 

 of the branches. .\6. rt Transverse section through a rhabdosome, showing tlie central coeno- 

 sarcal canal and its four longitudinal septa. .\6 (Copies from Holm) 



Diplograptus have now however been demonstrated to be not the result of the 

 coalescence of two branches, but of the budding of thecae of one seiies alter- 

 nately on opposite sides. It is, hence, evident that the two genera are of 

 entirely different structui'e. Subsequent observers, as Lapworth, Tullberg 

 and Tornquist, have all corroborated Hall's conception of Phyllogi'aptus, and 

 Tullberg recognized the close relationship between Totragraptus and Phyllo- 

 graptus. 



