152 



Cincinnati Society of Natural History. 



Arthropora, Ulrich. — Zoarium jointed, segments short, with several 

 branches or spurs projecting from each edge. Cell apertures sub cir- 

 cular, separated by interstitial pits or sulci, and occasionally closed by 

 an operculum. Lower Silurian. 



Dicranopora, Ulrich. — Zoarium jointed; segments divided dicho- 

 tomously at the upper end. Cell-apertures oblong, quadrate or ellip- 

 tical, arranged between elevated longitudinal lines. Lower Silurian. 



Clathropora, Hall. — Zoarium anastomosing and forming a regular 

 net-work. 



Family Stictoporidai, Ulrich. 



Zoarium not jointed, consisting of compressed branches or leaf-like 

 expansions, which are attached to foreign bodies by a continuousan d 

 expanded base. Branches and expansions composed of two layers of 

 cells grown together, as in the Ptilodictyoaidce, by the adhering of 

 their epithecal laminae. Interstitial cells, diaphragms, and opercula 

 often present. Vesicular interstitial tissue occasion ally developed. 



Stictopora, Hall. — Zoarium attached to foreign objects by a basal 

 expansion, which is continuous with the frequently branching frond 

 above. Edges of branches non-poriferous. Cell-apertures circular or 

 elliptical. Silurian, Devonian. 



Stictoporella, Ulrich. — Like the preceding, but smaller, cells ellipti- 

 cal, with two or more interstitial pits situated between the longer di- 

 ameters of the cell-apertures. Lower Silurian. 



Rhinidictya, Ulrich. — Zoarium narrow, branching at long intervals 

 Cells surrounded by a close series of small spiniform tubuli. Trenton 

 Cincinnati. 



Cystodictya, Ulrich. — Zoarium like that of Stictopora, but with 

 wider interstitial spaces. Sections show that the intertubular spaces 

 are occupied by a vesicular tissue. Sub-carboniferous. 



Phoenopora, Hall. — Zoarium forming simple, palmate, or irregularly 

 branching fronds, without a distinct non-poriferous edge. Cells ar- 

 ranged between elevated longitudinal lines. " Maculae'' often developed. 

 Trenton to Niagara. 



Pachydictya, Ulrich. — Zoarium composed of large, thick, somewhat 

 irregularly branching fronds. Cells ovate, separated by angular inter- 

 stitial tubes, which are closed by an interstitial membrane, and at in- 

 tervals form "maculae." Diaphragms are developed in both sets of 

 tubes. The median epithecal plates perforated by minute foramina, so 

 as to bring the two sides of the frond into connection. Trenton to 

 Lower Helderberg. 



