642 



Repoet of the State Geologist. 



I 



smooth or striated ; disposition of cell apertures variable ; in the 

 typical forms plumose, with longitudinal rows in the middle of 

 the frond, and oblique lateral rows diverging from those on each 

 side. Other species have longitudinal rows separated by ridges, 

 and still others have the apertures arranged in diagonally inter- 

 secting rows. 



Ptilotrtpa, Ulrich. 



(Geol. Sur 111., 7ol. YIII, p. 193. 1890.) 



Type, Ptilotryjpa obliquata, Ulrich. 



Original diagnosis. "Bifoliate, forming large ramose expansions. 

 Zooecial tubes and apertures very oblique. At the upper extrem- 



100. 



101. 



102, 





Fig. 100. Ptilotrypa ohliquata, natural size. 



Fig, 101. Vertical section, 'natural, size. 



Fig. 102. A portion of the surface enlarged. 



Fig. 103. Tangential section, showing usual characters and accessory pores. 



