406 PALAEONTOLOGY OF ILLINOIS. 



PHACELOPORA Ulrich. 



(For generic diagnosis see page 368.) 



PHACELOPORA PERTENUIS Ulrich. 



PI. XXIX, flg. l-lc. 



Zoarium articulated ; exceedingly slender, consisting of numer- 

 ous, elongate conical segments, arranged in linear series. Often 

 two segments are developed instead of one, when the zoarium 

 is diehotomously branched. Zooecia tubular, compressed coni- 

 cal, suboval in transverse section, with an average width of 

 0.12 mm., arranged in pairs, each pair constituting a segment; 

 apertures contracted, circular, about 0.06 mm. in diameter. 

 Sutures between zooecial tubes more sharply impressed on the 

 anterior side than on the posterior where the minute axial tube 

 is situated. Segments 0.6 to 0.8 mm. long, 8-shaped in cross- 

 section just below the apertures; here the lateral diameter is 

 from 0.2 to 0.25 mm. and the smaller about 0.15 mm., while 

 at the proximal extremity of each segment the diameter is only 

 0.07 mm. Segments are developed from the minute axial tube. 



This very interesting bryozoan is so unique, that no compar- 

 isons are required. Its thread-like zoarium is readily over- 

 looked. 



Position and locality: Upper beds of the Trenton group. 

 Thebes, 111. Rather rare, associated with several species of 

 Nematopora and Crinoids. 



PHACELOPORA CONSTRICTA Ulrich. 



PI. XXIX. flg. 2. 



Of this species I have seen only the fragment figured. This 

 consists of five short segments, having each the appearance of 

 being set into the expanded upper end of the one preceding it. 

 The segments vary slightly in length, but do not exceed 0.3 mm.; 

 the diameter expands from about 0.13 mm. below, to 0.25 mm., 

 or a little less, at the apertures. Each is composed of five 

 (possibly six) subcylindrical zooecial tubes, the sutures being 

 sharply impressed, and most of the slightly contracted circular 

 apertures apparently closed by a convex lid. The diameter of 



