BRYOZOA. :>,'.>:', 



<ii;Ai'T<uu<TYA I'lrich. Zoaria rising from a pointed articulat- 

 ing base into continuous dichotomously divided narrow fronds. 

 Zo'i'cia with sulK-ircular aperture, surrounded by a low pc-ris- 

 tome subpolygonal in outline. Inters] >ac>s depressed, generally 

 linear, sometimes with one or two fine tortuous elevated lines; 

 vertically lined in longitudinal sections, but with the lines in- 

 terrupted. Median lamina? straight in transverse sections. 



Type: G. pei-elegnns Ulrich. Range, Trenton to Cincinnati. 



ARTHROPORA Ulrich. Zoaria bushy, spread in a plane, coin- 

 posed of numerous segments; joints sometimes simple, usually 

 with several short lateral branchlets. some of which may be 

 tipped for articulation with succeeding segments. Zocecia with 

 elliptical or subpyriform apertures and elevated margins. In- 

 terspaces with one or more vermicular stria?. Apertures, when 

 perfect, closed by centrally perforated opercular structures. 

 Median lamina? zig-zag in transverse sections. 



Type: Stictoporti shnfferi Meek. Range, Trenton and Cincin- 

 nati. 



T.EMODHTYA ii. gnu. Zoaria growing from a basal expansion 

 into dichotomously divided narrow branches or broad fronds. 

 Zooecial structure very much as in some species of Ptilodictyn 

 (P. pavomn D'Orb.). Apertures elliptical or subcircular, sur- 

 rounded by a sloping area. Interspaces ridge-like. Both ''hemi- 

 sppta" present. 



Type: T. ramulosx n. sp. Range, upper Helderberg to St. 

 Louis. 



PIILOTRYPA n. gen. Zoaria forming large ramose expansions. 

 Zooecial tubes and apertures very oblique. At the upper ex- 

 tremity of the acutely ovate aperture there is a small cell which 

 is best seen in tangential sections. Surface with irregular, longi- 

 tudinally channelled spots. 



Type and only known species: P. obliquatu n. sp. Cincinnati 

 group. 



STICTOTRYPA n. gnu. Zoaria consisting of dichotomously di- 

 vided, narrow, compressed branches. Zooecial apertures circular 

 or elliptical, surrounded by a distinct, evenly elevated peristome. 

 Interspaces flat or concave, composed of horizontally laminated 

 solid tissue. 



Tvpe: Stictopora similis Hall. Range, Trenton to Niagara. 

 -49 



