664 



Report of the State Geologist. 



sometimes polygonal ; very frequently oblique to the surface, 

 alternating and imbricating, with frequent comparatively large 

 spines at the angles formed by the junction of the cell walls ; 

 surface with monticules having apertures larger than those on 

 other portions of the frond, the cell walls usually extending 

 above the surrounding surface. 



129 





Upper>ight-hand figs. Petigopora gregaria, a frond natural size and vertical section enlarged. 



Upper left-hand fig. Surface of same enlarged. 



Lower right-hand figs. P. asperula, natural size and vertrical section enlarged. 



Lower left-hand fig. Surface enlarged. 



Family Ceramoporellidae. 



Ceramoposella, Ulrich. 

 (Jour. Cin. Soc. ISTat. Hist., Yol. Y, p. 156. 1882.) 

 Type, Oeravioj)orella distincta, Ulrich. 



Zoarium incrusting, becoming massive by the superim position 

 of numerous thin layers; cell tubes short ; walls thin ; apertures 

 more or less oblique ; posterior portion of peristome strongly 

 elevated, cucullate, denticulate; mesopores abundant, often com- 

 pletely isolating the cell tubes ; surface with maculae destitute 

 of cell apertures, from which the cell apertures frequently 

 radiate in all directions. 



