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PALEONTOLOGY OF ILLINOIS. 



Fig. 2. a, Transverse section x50 of Ptilodictyavariabilis,* showing the basal portion 

 of the two layers of zocecia, and the duplex character of the median lamina; between 

 the plates there is no series of median tubuli. b, small portion of a tangential section 

 of Tceniodictya cingulata, x 50, showing a transverse lining of the central region of the 

 walls, a character often present among the PTILODICTYONID^;. c, deep tangential section 

 of Stictopora mutabilis, VI., x 50, showing the primitive portion of the zooscia and the 

 median tubuli in their walls. d, tangential section of same showing characters of zooecia 

 just beneath the superficial aperture. e, transverse section of a young example of same, 

 x 50, showing median tubuli. f, transverse section of old example of same, x 50. g, Ver- 

 tical section through one zooecium of an old example of same, x 50. h, vertical section 

 section of a young specimen of same, x 50. 



"This name is proposed instead of Ptilodictya nodosa for the form figured in my 

 "Amer. Pal. Bryozoa," under that name, Hall's Escharopora nodosa (Pal. N. Y. vol. 1, 

 1847.) having proved to belong to Ptilodictya, 



