386 PALAEONTOLOGY OF ILLINOIS. 



at short intervals till there is produced a broad frond per- 

 forated at rythmical intervals by circular or elliptical feuestrulcs. 

 In other respects like Cystodictya. 



Type: C. cycJops, Keyserling. Range. Upper Helderberg to 

 Carboniferous. 



DICHOTRYPA n. gen. Zoaria consisting of large, thin, bifoliate 

 expansions. The surface with solid macuke. Zocecial structure 

 in conformity with that given for the family. 



Type: D. foliata Ulr. Range, Niagara to St. Louis. 



ACTINOTRYPA n. gen. Zoaria very much as in Dlcliotryjm. 

 Zocecia apertures showing the projecting ends of from eight to 

 ten vertical septa-like ridges, that extend down on the inner 

 side of the tubular vestibule nearly or quite to the primitive 

 apertures. 



Type and only known species A. peculiaris (Fistulipora pecu- 

 liaris Rom.), of the Keokuk group. 



T.ENIOPORA Nich. Zoaria consisting of dichotomously divided 

 branches as in Cystodictya, but differing from that genus in 

 having a strongly elevated longitudinal central ridge on each 

 face, causing the transverse section of the branch to be diamond 

 shaped. The ridges may be obtusely angular, or sharp, thin 

 and prominent. The zooecia apertures are arranged in a pin- 

 nate manner or in longitudial rows, and increase in size out- 

 ward. 



Type: T. penniformis Nich. Hamilton group. 



PRISMOPORA Hall. Zoaria consisting of triangular branches 

 di-or trichotomously divided at irregular intervals; sides equal 

 or unequal, concave or flat, each celluliferous ; margins sharp, 

 straight or serrated, with a narrow solid border. In transverse 

 section the zooecia are seen to arise from internal laminap, which 

 radiate from the center to each angle, and divide the branches 

 into three subequal triangular portions. Apertures varying in 

 arrangment, frequently occupying the summits of small papillae. 

 Minute structures as given for the family. 



Type; P. triquetra Hall. Range, Upper Helderberg to Coal 

 Measures. 



