880 PALEONTOLOGY OF ILLINOIS. 



a few horizontal diaphragms are often present. Walls ap- 

 parently minutely porous, composed of irregularly laminated 

 tissue. 



CERAMOPORA Hall. Zoaria discoidal; free or attached by the 

 center of the base to foreign bodies. Under surface with one or 

 more layers of small, irregular, inter-communicating cells, which 

 do not form tubes. Zooecia large, oblique, imbricating, ar- 

 ranged in a radial manner around the depressed center, com- 

 municating with each other and the mesopores by means of 

 remote perforations in their walls. Mesopores irregular, short, 

 numerous at the center of the colony, decreasing in number 

 toward the margin. 



Type: C. imbricata Hall. Niagara group. 



CERAMOPORELLA Ulrich. Zoaria incrusting, becoming massive 

 by super-imposition of numerous thin layers. Zooecial tubes 

 short, the Vails thin. Apertures more or less oblique, hooded, 

 commonly of oval shape. The hoods are directed away from 

 the centers of small maculae marking the surface at rythmical 

 intervals. Mesopores abundant, often completely isolating the 

 zooecia. In the fully matured state their apertures are closed 

 by a thin membrane. Diaphragms occasionally present in the 

 z official tubes. 



Type: C. distinct^ Ulrich. Range, Trenton to Niagara.? 



CREPIPORA Ulrich. Usually incrusting, sometimes lamellate or 

 massive, with a wrinkled epitheca on the lower side; in one 

 case forming regular hollow branches. Surface exhibiting, at 

 subregular intervals, maculae of mesopores, appearing as min- 

 utely porous or subsolid elevations or depressions. Zooecia very 

 little oblique, the apertures varying from rhomboidal to sub- 

 pyriform. Lunarium well marked in perfect examples, but 

 easily overlooked when a little worn; best shown in tangential 

 sections. Mesopores usually restricted to the macula?. Dia- 

 phragms are developed in moderate numbers. 

 Type: C. simulans Ulrich. Range, Trenton to Upper Silurian. 



DIAMESOPORA Hall. (Coeloclema Ulrich). Zoaria ramose, 

 branches hollow, lined internally with a striated epitheca. Sur- 

 face with or without maculae. Zooecia with rather thick walls, 

 and sub-oval apertures. Peristome complete, but highest at 



