402 PALEONTOLOGY OF ILLINOIS. 



tures regularly arranged, oval or circular, placed at the bot- 

 tom of a sloping area, rhombic or hexagonal in outline, or 

 between straight or fiexuous longitudinal ridges. Acanthopores 

 and smaller spines generally present, but mesopores are absent. 



RHOMBOPORA Meek, (Orthopora Hall.) Zoaria slender, ramose, 

 solid. Zooecia with the vestibular or outer portion thick- 

 walled. Apertures arranged regularly in diagonally intersecting 

 or longitudinal lines. Strong acanthopores often present at the 

 angles of junction and more numerous, smaller spines, generally 

 occupy the summit of the ridge-like interspaces between the sub- 

 elliptical apertures. Diaphragms sometimes present in the axial 

 region. 



Type: R. lepidodendroides Meek. Range, Niagara to Upper 

 Coal Measures. 



RHABDOMESON Young and Young. This genus differs from 

 Rhombopora only in having a slender axial tube, to which the 

 proximal ends of the zocecia are attached. 



Type : Millepora gracilis Phillips. Carboniferous. This genus 

 is not known from American deposits. 



CCELOCONUS n. gen. Zoaria simple, hollow, expanding grad- 

 ually from the striated and sub-acute basal extremity; sub- 

 stance thin. External characters of zocecia as in Rhombopora; 

 primitive portion short. Hemisepta well developed. 



Type: C. rhombicus n. sp. Range, St. Louis to Chester. 



NEMATAXIS Hall. Upper Helderberg and Hamilton. 



AOANTHOCLEMA Hall (pars.) Upper Helderberg to Warsaw. 



BACTROPORA Hall. Zoaria simple, unbranched, the lower ex- 

 tremity pointed. In other respects like Rhombopora. 



Type: B. granistriata Hall. Upper Helderberg to Keokuk. 



(?) TROPIDOPORA Hall. Upper Helderberg. 



Family STREBLOTRYPIDJE Ulrich. 



Zoaria variable. Zorecia with the primitive portion sub-tub- 

 ular or tubular; apertures sub-circular, often truncated pos- 

 teriorly, surrounded by a slightly elevated rim. Front, or 

 outer surface of cell back of the aperture, simply depressed, or 

 with from two to twelve or more small pits. Diaphragms 

 wanting. 



