582 



Eeport of the State Geologist. 



portion of the length of the cell tubes, their walls are very thin, 

 and diaphragms remote or entirely wanting. Near the surface 

 the walls become thickened and the diaphragms are numerous ; 

 surface with frequent maculae of cell apertures larger than those 

 on other portions of the frond. 



Fig. 154. 3Ionotrypella cequalis surface, xl8, 

 Fia. 155. Transverse section of same, xl8. j 

 Fig. 156. Vertical section, xl8. 



1890.) 



Petalotrtpa, Ulrich. 

 (Geol. Sur. Ill, Yol. YIII, p. 377. 

 Type, Petalotrypa compressa, Ulrich. 



Zoarium bifoliate, consisting of irregular compressed branches 

 or simple fronds ; celluliferous on both sides ; cell tubes prismatic, 

 arising from a strongly flexuous mesotheca ; apertures polygonal. 

 This genus may be distinguished from the other forms of this 

 family by its bifoliate mode of growth, and the presence of a 

 mesotheca. 



Fig. 157. Petalotrypa compressa, zoarium natural size. 

 Fig. 158. Transverse section of same, xl8. 

 Fia. 159. Vertical section, xl8. 



