Genera of the ]N'orth American Palaeozoic Bryozoa. 585 



layers of growth ; rarely parasitic, generally free with a radiately 

 and concentrically striated epitheca on the lower side ; typically 

 composed according to age of from one to many subequal parts, 

 each part gently convex, with the cell apertures increasing in size 

 from their margins to their centers ; cell tubes with very infre- 

 quent diaphragms and more numerous cystiphragms ; mesopores 

 numerous, closely tabulate ; surface with spiniform nodes. 



1883.) 



Atacioporella, Ulrich. 

 (Jour. Gin. Soc. Nat. Hist., Yol. YI, p. 247. 

 Type, Atacioporella typicalis^ Ulrich. 



Zoarium generally forming thin crusts over foreign bodies, 

 rarely lobate or subramose ; surface with monticules and very 

 closely resembling some forms of Ceramoporella. 



165 



166 



167 



Fig. 165. Atacioporella typicalis, surface, xl8. 

 Fig. 166. Transverse section, xl8. 

 Fig. 167. Vertical section, xl8. 



Cells with very thin inflected walls ; apertures oval, but the 

 numerous nodes at their margins give to them an irregular 

 74 



