390 PALAEONTOLOGY OF ILLINOIS. 



Type: E. serrata Ulrich. Range, Hamilton group. 



PACHYDICTYA Ulrich. Zoaria varying from parallel margined 

 narrow branches to large undulating expansions. The edges 

 are acute and have a non-celluliferous border. In the larger 

 species the surface exhibits solid granulose maculae. Zooecia 

 rising rather abruptly from the mesial laminae, near which they 

 have very thin walls, are broad elliptical or subquadrate in out- 

 line, arranged in longitudinal series and partially separated 

 from each other by small vesicles. Toward the surface their 

 walls are thickened, ring-like, and usually completely isolated, 

 and the interspaces solid. Median tubuli well developed between 

 the mesial laminae, and in one or two rows between the zooecia. 

 Apertures plain or with slight peristome. Diaphragms cross 

 the zooecia tubes. 



Type : P. robusta Ulr. Range, Trenton to Lower Helderberg. 



PHYLLODICTYA Ulrich. Zoaria leaf-like, or consisting of irregu- 

 lar broad branches. Zooecia tubular, the prostrate portion 

 long; apertures circular, slightly oblique, with the posterior 

 margin elevated. Interspaces wide, solid, granulose, traversed 

 vertically by numerous minute tubuli. A few diaphragms pres- 

 ent. 



Type: P. frondosa, Ulr. Range, Trenton. 



Family PTILODICTYONID.E Zittel. 



Zoaria segmented or continuous, bifoliate. Zooecia sub-tubular, 

 the primitive cell more or less elongated, subquadrate, rhombic, 

 or hexagonal in outline, with thin walls. Both superior and 

 inferior hemisepta generally present. Vestibular portion with 

 thick and often ring-like walls, the central region between the 

 cavities usually of conspicuously lighter or darker color than 

 the rest. When wide the region usually appears transversely 

 lined; at other times occupied by untabulated mesopores. 

 Median tubuli wanting. 



PTILODICTYA Lonsdale. (Escharopora Hall, Heterodict.va 

 Nich.) Zoaria segmented, consisting of a small, radially striated 

 basal expansion which is attached to foreign bodies, and has 

 at the center of the upper surface a socket for articulation with 

 1lie sub-solid extremity of the erect and unjointed frond. Frond 



