NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
121 
avicularia are interopesial, very small, elliptical, little raised. The ancestrula is 
very small. 
Measurements . — Opesiaj 
t 
ho— 0.2T-0.30 mm. 
fo=0.16-0.18 mm. 
n . Zs=0.40 mm. 
Zooecia 7 A 0 . 
[fc=0.24 mm. 
Variations.— A. remarkable phenomenon in this species is the dimorphism of 
the mural rim. On the same zoarium, without any apparent reason, there are 
mural rims thin and distinct, and others thick and confluent. The first are devoid 
of dietellae while the second have five of them. These small pore-chambers are 
not therefore indispensable to the life of all the zooecia of the same zoarium, and 
not even to the passage of the mesenchymatous fibers. The ancestrula is very 
small. Around it the zooecia have always a separate mural rim and are not 
always accompanied by avicularia. The same holds true on the zoarial margins. 
We have not observed regenerated zooecia. 
Affinities . — This species differs from M embrendoecium rectum in its confluent 
mural rims not enlarged at the base and in its very inconspicuous avicularia. The 
specimen figured from Cambridge. Georgia, is altered chemically, as are most of 
the specimens from this locality. 
Occurrence . — Upper Jacksonian (Ocala limestone) : Bainbridge, Georgia; Bed 
Bluff, on Flint Biver, 7 miles above Bainbridge, Georgia (rare) ; west bank of 
Sepulga Biver, Escambia County, Alabama (rare) ; Chipola Biver, east of Mari- 
anna, Jackson County, Florida (rare). 
Middle Jacksonian: Baldock, Barnwell County, South Carolina (rare); 18 
miles west of Wrightsville, Johnson County, Georgia (very rare). 
Lower Jacksonian (Moodysmarl) : Jackson, Mississippi (very rare). 
Cotypes. — Cat. Nos. 63889-63892, U.S.N.M. 
MEMBRENDOECIUM LOWEI, new species. 
Plate 81, fig. 1. 
Description . — The zoarium incrusts small pebbles, from which it becomes easily 
detached. The zooecia are elongated, elliptical, distinct, or confluent; the mural 
rim is broad, flat, granulose. The opesium is elliptical or oval, the narrow end 
proximal. The ovicell is a very small, distal convexity. The avicularia are very 
indistinct and not prominent. 
M easurements . — Opesia 
\ho— 0.20 mm. 
[?<?— 0.12 mm. 
Zooecia 
| L, 2=0.30 mm. 
1 1, z =0.20-0.22 mm. 
Affinities . — The mural rims are very often united, so that the boundary between 
the zooecia is little visible. It is impossible to say whether the avicularia are 
indeed present or if these are only interopesial cavities. If, therefore, our observa- 
tion of the endozooecial ovicells should not be confirmed, it would be necessary to 
place this species under Conopeum. 
M embrendoecium lowed differs from M. duplex in its smaller micrometric 
dimensions and in its inconspicuous avicularia. 
