556 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Genotype. — Meniscopora bigibbera, Gregory, 1893. 
Range. — Thanetian-Helvetian. 
I 
MENISCOPORA SUBPLANA Ulrich, 1901. 
Plate 2, figs. 4. 5. 
( 
1901. Lepralia subplana Ui.kich, Maryland Geological Survey, Eocene, p. 219, pi. 59, 
figs. 17, 18. 
Original description.- — ■“ Zoarium, as seen in three specimens, forming a hollow 
cylinder, composed of numerous layers, each 0.3 to 0.35 mm. in thickness, and 
varying in diameter according to the number of lai'ers from 7 to 13 mm. Zooecia 
not very regularly arranged, sometimes subovate, at other times hexagonal or 
subquadrate, longer than wide, the length averaging about 0.45 mm. Upper sur- 
face nearly flat, the outline of the zooecia, in aged conditions especially, scarcely 
distinguishable and mainly by a double row of pores which, as shown by frac- 
tures, are the mouths of small tubes transversing the wall in a vertical direction. 
Front wall slightly convex, perforated, the pores usually smaller than those 
outlining the zooecia, distinctly visible on the inner surface, sometimes wanting 
over a varying space just behind the aperture. The latter is rounded in front, 
nearly straight behind, with the angles rounded, generally semielliptical, the 
width and length averaging, respectively, 0.15 and 0.13 mm. Small round or 
oval avicularia generally present. Their position is variable, though usually close 
to the rim of the aperture. While an occasional zooecium may occur, having no 
avicularia, as many or more will be found having one on each side of the aperture. 
Ooecia unknown. 
Fractures dividing the zooecia vertically (fig. 4) show that the walls (side 
and front) are traversed by minute, wavy, vertical tubuli, and that the zooecial 
cavities are connected by two series of pores, the larger set near the bottom and 
a row of smaller pores above the midheight. The openings of the larger set are 
often irregularly distributed over the concave floors of the zooecia.” 
Ulrich’s description is quite exact. The zoarium is multilamellar and incrusts 
algae; the lower face, in contact with the substratum is smooth or ornamented 
with numerous small hydrostatic tuberosities. 
In the interior, the areolar cavities are quite visible. 
The gonoecia are identical in form with the other zooecia. but they are some- 
what larger. 
Occurrence . — Lowest Eocene (Bryozoan bed at base of Aquia formation) : 
Upper Marlboro, Maryland (not uncommon). 
MENISCOPORA ELL1PTICA, new species. 
Plate 97, figs. 17-21. 
Description . — The zoarium is an Eschara form composed of two lamellae 
placed back to back and easily separable. The zooecia are little distinct, elon- 
gated, straight ; the frontal somewhat convex bears some pores which are little 
