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 zoarium (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, 1S79. 
A. Oriented zooecia, X 25. B. Cumulate zooecia, X 25. C. Operculum, X 85. D. Apertura, 
X 85. E, F. Avicularian 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: hut 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. 4). 
In the tangential sections (figs. 11, 12, 14) the zooecia are separated by white 
lines caused by the frontal convexity. The olocvstal elements (figs. 12, 14) are 
