Genera of the ^N'ortii American Palaeozoic Bryozoa. 557 



observed near the margin of the frond), the cell tubes are very 

 short, the apertures oval^ closely and irregularly disposed ; per- 

 istomes promineat, the posterior portion strongly elevated ; 

 interapertural space smooth, flat or slightly concave. As the 

 growth continues the posterior portion of the peristomes becomes 

 more elevated, and those of adjacent apertures are united by 

 thin irregular connecting walls, which traverse the interapertu- 

 ral spaces, and gradually form an elevated and very irregular net- 

 work, which at numerous points is further elevated into strong 

 spines. The apertures of some of the cell tubes occupy one side 

 of the bottom of the large depressions ; while others have grown 

 with the net- work, and are on a level with numerous, irregularly 

 distributed, angular and smaller cells, probably corresponding to 

 the vesicular tissue of the immature type. 



Family Selenoporidae. 

 This family includes the forms similar to Lichena ia, but hav- 

 ing the cell apertures enclosed in a vestibular area formed by the 

 coalescence of thin prominent plications. 



Selenopoea, Hall. 

 (Pal. ]Sr. Y., Yol. Yl, p. xvii. 1887.) 



Type, Selenopora circincta, Hall. 



(Plate 24, figs. 4-7.) 



Zoarium forming incrusting expansions. Cells tubular, oblique 

 to the surface, pseudo-septate ; frequently alternating and imbri- 

 cating ; apertures circular or slightly oval ; anterior p >rtion of 

 peristome slight or entirely wanting ; posterior portion strocgly 

 elevated, denticulated, projecting over and partially concealing 

 the aperture. The posterior portion of the peristomes are con- 

 nected by prominent oblique walls, which traverse the surface 

 between the apertures, uniting and forming polygonal vestibular 

 areas ; the cell apertures being situated on the posterior portion 

 of the floor of the area ; surface with flat circular maculae des- 

 titute of cell apertures. The cell apertures adjacent to these 

 maculae, and radiating from them, are larger and more oblique 

 than those on other portions of che frond ; intercellular structure 

 the same as in Fistulipuea. It is distinguished from the Odo^to- 



