NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
801 
ornamented with large vacuoles. The peristome is salient, thin, elliptical, or oval. 
The dorsal is very porous; the longitudinal sulci are of little depth, the nervi 
are wide but little convex; the vacuoles are large but of lesser dimensions than 
the frontal vacuoles. 
Diameter of the peristome 0.10 mm. 
Diameter of the aperture 0.06-0.08 mm, 
i easwements. • p)] s ^ ance between the peristomes 0.50 mm. 
Separation of the peristomes 0.14 mm. 
Variations . — The peristome is very salient (fig. 8) or scarcely projecting (fig. 
10). When the frontal vacuoles are smaller (fig. 10) they are more numerous. 
The dorsal is exceedingly variable and it is impossible to discover the rule of varia- 
tion. However, on the young branches the sulci are very narrow and the nervi 
very wide (fig. 11) . Somewhat later the vacuoles are more visible (figs. 13, 15). 
Normally (fig. 12) the vacuoles are large and the nervi little salient. 
A, B. Frontal, X 12, and dorsal, X 8, of Crassohornera ( Ceriopora ) arlmscula Reuss, tlie 
latter showing the ovicell. 
C-E. Views of the zoarium, natural size, and the frontal and dorsal, X 25, of Crassohornera 
icaipukurensis Waters, 1887. 
The dorsal vacuoles are enlarged at their extremity, for in tangential sections 
they appear smaller (fig. 17). As in all the species of the genus the elements are 
thick and crowded which makes it very difficult to obtain good thin sections 
(fig. 19). 
The squamous and lamellar structure of the walls appear to result from the 
linear union of the primitive elements (fig. 18). 
Affinities . — The species singularly resembles Ilomera froncliculata Lamou- 
roux, 1821, in the number of frontal vacuoles and in the elliptical form of the 
peristomes. It differs from it, however, in a smaller number of longitudinal sulci 
55899— 20— Bull. 104 
-51 
