872 PALEONTOLOGY OF ILLINOIS. 



restricted to the monticules or maculae. Acanthopores originat- 

 ing in the axial region, sometimes very large, in other cases 

 more numerous and smaller. Apertures closed at intervals by 

 a thin calcareous pellicle. 



Type: D. aspera Edwards and Hairne. Range, Trenton to 

 Hamilton. 



PETIGOPORA Ulrich. Zoaria parasitic, with a narrow non-po- 

 riferous band along the outer margin. Mesopores absent. 

 Acanthopores well developed, abundant. 



Type: P. gregaria Ulr. Range, Trenton to Cincinnati. 



DEKAYELLA Ulrich. Ramose, branches sometimes compressed. 

 Mesopores more or less numerously distributed among the 

 zocecia, and often aggregated into irregular "maculae." Acan- 

 thopores of two sizes, the smaller ones the most abundant and 

 only present in the peripheral region. Those of the large size 

 commence in the axial region. Diaphragms horizontal. 



Type: D. obscura Ulr. Cincinnati group. 



Family CALLOPORIDJE, n. fam. 



Zoaria ramose, sub-frondescent, or discoidal. Zooecia gener- 

 ally sub-circular, rarely polygonal, separated from each other 

 more or less completely by angular mesopores. Walls usually 

 thin, sometimes thickened and ring-like in transverse section. 

 Apertures closed by centrally perforated covers, which, as 

 growth proceeds, are left behind in the tubes to form the floors 

 of the succeeding chambers. Acanthopores wanting in the typi- 

 cal forms, very small when present. 



CALL/OPORA Hall. Ramose to sub-frondescent, or sub-pyriform, 

 smooth or tuberculated. Zooecia with thin walls varying, 

 according to the number of mesopores, from circular to poly- 

 gonal. Apertures in the perfect state closed by opercular covers; 

 perforation small, central, generally surrounded by radiating 

 ridges. Mesopores angular or rounded, more or less numerous, 

 sometimes completely isolating the zooecia, with crowded dia- 

 phragms. Zooecial tubes slowly attaining their full development, 

 closely tabulated near their origin in the axial region; the dia- 



