682 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
HETEROPORA TECTA Ulrich, 1901. 
Plate 104, figs. 14-20. 
1901. Heteropora ? tecta Ulrich, Maryland Geological Survey, Eocene, p. 210, pi. 59, 
figs. 15, 16. 
Description . — The zoarium is subcylindrical, solid or hollow. The orifices are 
orbicular and measure 0.10 mm. in diameter. The mesopores are polygonal, wide 
open, as large as the tubes. The tubes have vesicular walls at their extremity. 
The small number of specimens found does not permit a more complete study. 
The various aspects of this species are shown in Ulrich’s figures, which we produce, 
and in our new illustrations. 
Occurrence . — Lowest Eocene (Bryozoan bed at base of Aquia formation) : 
Upper Marlboro, Maryland (rare). 
Plesiotype. — Cat. No. 65458, U.S.N.M. 
HETEROPORA ALVEOLATA, new species. 
Plate 111, figs. 1-4. 
Description . — The zoarium is massive and gives forth cylindrical branches. 
The apertura is large, hexagonal, and measures 0.16 mm. in diameter. The meso- 
pores are irregular, polygonal, and are often closed by a calcareous pellicle. In 
sections, the tubes are cylindrical, traversed by diaphragms which become very 
numerous at their extremity in the region of the mesopores; the walls are quite 
thick and are formed of a continuous series of very large vesicles. The mesopores 
are long and have diaphragms. 
I Diameter of the apertures 0.16 mm. 
Distance between the apertures 0.30-0.40 mm. 
Diameter of the branches - 3.00 mm. 
Affinities . — The diaphragms are so numerous that they give to the longitudinal 
section an alveolar aspect absolutely characteristic and very peculiar. However, 
such a structure is not rare in the Paleozoic formations. The section does not 
always cut exactly across the mesopore ; when it cuts only through the wall it re- 
veals a complicated structure resulting from the coalescence of the sectioned 
vesicles. 
This species differs from Heteropora ovalis in the form of its aperture and in 
the great number of its diaphragms. 
O ccurrence .— Midway an (Clayton limestone) : Mabelvale, near Little Rock, 
Arkansas (rare). 
Holotype. — Cat. No. 65254, U.S.N.M. 
HETEROPORA OVALIS, new species. 
Plate 150, figs. 1-6. 
Description . — The zoarium is free, branched, arborescent or dichotomous; the 
branches are cylindrical. The apertures are somewhat oval, slightly salient, and 
