46 AMERICAN FOSSIL BRYOZOA. [bull. 173. 



Ph^nopora Hall. 



Like Ptilodictya, except that there are two mesopores in each inter- 

 space between the ends of the apertures. 



Genotype: PJicenopora explanata Hall. Ordovician, Silurian, 



Fourteen species. 



Arthropora Ulrich. 



Zoarium bushy, composed of numerous articulating equal segments, 

 spread in a plane; apertures elliptical, surrounded by a delicate peri- 

 stome; interspaces with one or more thread-like ridges variously dis- 

 posed, and with a row of minute papillae. 



Genotype: Stictopora {Ptilodictya) shafferi Meek. Ordovician. 

 Five described and four new species. 



Graptodictya Ulrich. 



Zoarium a narrow bifurcating frond with a pointed base articulating 

 with a small basal expansion; apertures subcircular, surrounded by a 

 peristome subpolygonal in outline; interspaces depressed, usually with 

 one or two fine tortuous elevated lines. 



Genotype and only known species: Ptilodictya elegans Ulrich. 



Ordovician. 



Stictoporina Hall. 



Zoarium a simple or branching frond, from an obtusely pointed, 

 articulating base; apertures oval, in decussating series, inclosed in 

 rhomboidal or polygonal areas; interspaces elevated, angular. 



Genotype: Trematoporacla/viformis YlviW. Devonian. Three species. 



Family STICTOPORELLIDiE. 



This family differs from the Ptilodictyonidte mainly in that the 

 zoarium is not articulated, but grows upward from, and is continuous 

 with, a spreading base. 



Stictoporella Ulrich. 



Zoarium branching, cribrose, or leaf -like; zooecia with the primitive 

 portion tubular, usually long, generally without hemisepta, the inferior 

 one only occasionally present; orifices at the bottom of a wide, sloping 

 vestibule; thick-walled, un tabulated mesopores occur between the 

 apertures and line the margins of the zoarium. 



Genotype: Stictoporella interstmcta mv\(:\i = Ptilodictya flexuosa 

 James. Ordovician. Nine described and four new species. 



Ptilotrypa Ulrich. 



Zoarium ramose, with compressed or frondescent branches; surface 

 with irregular longitudinally channeled areas appearing like maculae; 



