580 



Report of the State Geologist. 



ally diverging for about two-thirds of their length, then abruptly 

 turning outward, the walls, previously very thin, becoming much 

 thickened. In the axial portion of the cells the diaphragms are 

 very infrequent or entirely wanting. In the peripheral portion 

 they are closely disposed; surface with numerous monticules 

 subregularly disposed in intersecting rows, occupied by cell 

 apertures larger than those on other portions of the frond. 



l^umerous species have been placed in this genus, but with one 

 exception they are not cogeneric with the type species. The 

 mesopores spoken of by various authors are not mesopores, but 

 joung cells, there being no mesopores in the type species. 



Lepiotrypa, Ulrich. 

 (Jour. Cin. Soc. ISTat. Hist., Yol. YI, p. 168. 1883.) 

 Type, Leptotrypa minima^ Ulrich. 



"Zoarium varying from thin incrustations to free forms of 

 discoidal, spiral or elongate-spiral shape ; irregular massive speci- 

 mens also occur; cells polygonal, with thin walls and a variable 

 number of delicate diaphragms ; cell walls appreciably thickened 

 in the peripheral region ; spines or acanthopores small, more or 

 less numerous, but usually restricted to the angles of junction 

 between the cell tubes." 



150 



149 



Fig. 148. Leptotrypa semipilans. A frond and vertical section, natural size. 

 Fig. 149. Vertical section of same, xl8. 

 iFiG. 150. Transverse section, xl8. 



