NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
69 
We have avoided the use of these archaic terms in our descriptions save 
Eschara, Lunulites, and Vincularia. 
The causes of zoarial variations are unknown. 
The free zoaria very seldom remain intact in fossilization and we most always 
find them in the state of minute fragments. When the latter are very numerous it 
is always interesting to attempt their restoration. Those which we have made 
Fig. 15. — Structure of the vestibular arch, etc. 
A. Membrendoecium rectum, new species, X 20. Calcified zooecia. 
B. Hinclcsina vicksburgica, new species, X 20. Opesium not completely covered by calci- 
fication. 
C. D. Harrneria diapliana MacGillivray, 1879. C. The distal half of a zooecium, the frontal 
wall of which has been removed, so that the highly developed vestibular arch may be seen and 
the rods by which it is connected with the lateral walls, X 55. D. The distal half of a zooecium, 
seen from the basal surface after removal of the basal wall. The basal wall of the vestibular 
arch is seen, X 55. (After Levinsen, 1909.) 
E. Vestibular arch of Mucronella peachi Johnston, 1847, X 50. (After Busk, 1854.) 
F. Diatoms and radiolaria found in the digestive apparatus of Chaperia spinosa Quoy and 
Gaimard, 1824. (After Jullien, 18S8. ) 
belong to species branching in a single plane and were relatively easy. We yet do 
not know how to restore the bushy zoaria. 
Habitat . — The bryozoa live — first, in deep water; second, in waters always 
clear and limpid; and, third, in waters constantly agitated superficially by tempests 
and deeply stirred by currents. (D’Orbigny, 1S50.) 
