BRYOZOA. 653 



nodes (? acanthopores) enclosing the sloping area at the bot- 

 tom of which the aperture is situated. Area deep, oval or sub- 

 rhombic in outline. Apertures oval, 0.17 mm. long by 0.09 

 mm. wide, with five in 2 mm. diagonally. About thirteen of 

 the transverse rows occur in 5 mm. 



Thin sections show that the zooecial tubes are arranged in a 

 wedge-shaped manner about the center, and that the nodes are 

 really the surface projections of thick-walled tubes. 



This species resembles R. dichotomy, of the Burlington lime- 

 stone, but is distinguished superficially by its larger zooecia, 

 smaller apertures, and deeper area. 



Position and locality: Keokuk group. Not uncommon at 

 King's Mountain, and Button Mould Knob, n6ar Louisville, Ky. 



i , 



RHOMBOPORA VARIANS Ulrich. 



PI. LXXI, flg. l-lb. 



Zoarium consisting of robust stems, 2 to 4 mm. in thickness, 

 which arise from an irregularly porous basal expansion, and 

 usually branch dichotomously at variable intervals. Angles of 

 bifurcation more or less wide. Zooecia apertures arranged in 

 diagonally intersecting and longitudinal series, with seven in 2 

 mm. measuring diagonally, and fifteen or sixteen in 5 mm. verti- 

 cally. Interspaces decreasing somewhat in thickness from below 

 upward, and varying considerably in character at the two 

 extremes, the extent of the variability depending upon the age 

 of the specimen. On the distal or young portions of the zoarium, 

 the interspaces are ridge-shaped, with the summit sharply de- 

 fined and carrying a single series of minute granules. The area 

 is elongate hexagonal in outline, 0.24 by 0.33 mm., with the 

 ends truncated, and slopes with moderate rapidity down to the 

 oval aperture, which has a length of 0.12 or 0.13 mm. Toward 

 the base the interspaces gradually loose their angularity, the 

 granules increase in number from one to two, and then three irreg- 

 ular rows, while the apertures become more nearly circular, and, 

 near the expanded base of the zoarium, may even be surrounded 

 by a faint peristome, the interspaces having ere this become 

 perfectly flat. 



Vertical sections show that the primitive or immature region 

 of the zooecial tubes may be intersected by an occasional thin 



