NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



615 



Variations. Most of the time the zooecia are oriented; nevertheless the species 

 is quite variable. The young zooecia (fig. 7) and the cumulate zooecia (fig. 10) 

 on the same zoariiun (fig. 6) have a thin and gibbose frontal wall. These gibbosi- 

 ties are much smaller on the zooecia with thick frontal (fig. 2) and are placed 



FIG. 184. Cellepora sardonica Waters, 1879. 



A. Oriented zooecia, X 25. B. Cumulate zooecia, X 25. O. Operculum, X 85. D. Apertura, 

 X 85. E, F. Avieularian mandibles, X 85. (A-F after Waters, 1879 and 1885.) 



between the avicularia. We have nothing to prove that the perforations of the 

 frontal are really avicularia and contain neither denticle nor pivot: but on the 

 genotype there are some true avicularia with pivot. The peristomial avicularium 

 is very curious; it is placed obliquely (fig. 5) and is little visible exteriorly: it bears 



FIG. 185. Cellepora janthina group. 



A-E. Cellepora janthina Smitt, 1867. A. Group of zooecia, X 25. B. A single zooecium, 

 X 50. C. Operculum, X 85. (A-C after Waters, 1899.) D. Group of ovicelled zooecia. 

 E. Operculum. (D, E after Norman, 1909, as Cellepora rotundora.) 



the habitual lyrula. The porous area of the ovicell is of a unique type; it is formed 

 by a much branched spine forming a sort of filtering apparatus and breaking very 

 easily (fig. i). 



In the tangential sections (figs. 11, 12, 14) the zooecia are separated by white 

 lines caused by the frontal convexity. The oloeystal elements (figs. 12, 14:) are 



