Geneea of the Xorth Americax Palaeozoic Bryozoa. 541 



Family Ptilodictyidae, Zittel, emend. 



The genus Ptilodiotya includes those forms which are pointed 

 below, articulating into a spreading base ; unbranched ; straight 

 or curved ; but other genera are included in this family whose 

 structure and mode of growth is the same as that of Piilo- 

 DioTYA, except that they are bifurcating. 



The following genera are included in this family : Geapto- 



DIOTYA, Pfl^NOPORA, PfILOD:OTTA, SxiCrOPOKINA and StIOTOTKTPA. 



Graptodiotya, Ulrich. 

 (Jour. Cin. Soc. JSTat. Hist., Yol. Y, p. 165. 1892.) 

 Type, Graptodiotya per elegans^ Ulrich. 



'' Zoarium arising from a pointed articulated base into continu- 

 ous dichotomously divided narrow branches ; zooecia with sub- 

 circular apertures surrounded by a low peristome ; subpolygonal 

 in outline ; interspaces depressed, generally linear ; sometimes 

 with one or two fine, tortuous, elevated lines ; vertically linear in 

 longitudinal sections, but with the lines interrupted." (Ulrich.) 



PflAENOPORA, Hall. 



(Pal. :^. Y., Yol. II, p. 46. 1852.) 

 Type, Phcenopora explanata, Hall. 



(Plate 15, figs. 8-10.) 

 Bryozoan forming thin, broad or ensiform expansions, cellulifer- 

 ous on each face ; cell apertures oval, separated by ridges, and 

 having two minute pits between the ends of adjacent apertures. 

 This genus has a very close resemblance to the typical forms of 

 Ptilodiotya, but is separated from them by the presence of inter- 

 apertural pits, which is a constant feature. 



Ptilodiotya, Lonsdale. 

 (Murch. Silurian System, p. 676. 1839.) 

 Type, Ptilodictya lanceolata, Lonsdale. 

 (Plate 15, figs. 4-7.) 

 Bryozoum consisting of a radially striated basal expansion, 

 attached to foreign bodies, and which has at the center of the 

 upper surface a socket for articulation with the subsolid extremity 

 of the erect and conjoined frond ; frond commonly lanceolate or 

 falciform unbranching ; margins of frond acute, noncelluliferous, 



