NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
137 
The granulations of the mural rim are extremely fine; the granules become 
larger by chemical changes (pi. 27, fig. 16). The ovicell is smooth in the Jack- 
sonian specimens (pi. 27, figs. 3, 7), but it is ornamented with a frontal callosity in 
those from the Vicksburgian (pi. 27, figs. 16, 17). This structure is always placed 
above the distal septula (pi. 28, fig. 6). The ovicells on the same zoarium are rare, 
and their occurrence in groups is very infrequent (pi. 27, fig. 9). Regenerated 
zooecia are rather rare (pi. 27. fig. 14). The opesial denticles are always irregular 
in form, size, and position; sometimes they are quite large (pi. 27, fig. 18). 
The zoarium is often unilamellar, either by splitting in half or by growth on 
algae (pi. 27, fig. 19). This variation affects all the specimens from the Vicks- 
burgian along the west bank of Conecuh River, Escambia County, Alabama. We 
have also some specimens incrusting shells from the Jacksonian at Wilmington, 
North Carolina. 
The dorsal lamella of each zooecium is an olocyst with scattered elements (pi. 
28, fig. 3). The mural rim and the cryptocyst are of the same nature and are 
formed by an olocyst in which the elements are grouped in radial lines (pi. 28, fig. 
2). The zooecial walls are t’ery thin (pi. 28. fig. 4) or very thick (pi. 28, fig. 5). 
By rubbing away the surface it is easy to bring out the two pairs of lateral septulae 
and the large distal septula (pi. 28, fig. 5). On the same zoarium the micrometric 
measurements are rather constant, but they vary much according to the locality. 
They may be small (pi. 27, fig. 10) or large (pi. 27, figs. 5. 8, 14). 
Occurrence. — Vicksburgian (Marianna limestone) : Salt Mountain, five miles 
south of Jackson, Alabama (very common) ; near Claiborne, Monroe County, Ala- 
bama (very common) ; west bank of Conecuh River, Escambia County. Alabama 
(very common) ; Murder Creek, east of Castlebury, Conecuh County, Alabama 
(very common) ; 1 mile north of Monroeville, Alabama (very common). 
Upper Jacksonian (Ocala limestone) : West bank of Sepulga River. Escambia 
County, Alabama (rare) ; Chipola River, east of Marianna. Jackson County, 
Florida (very rare). 
Jacksonian (ZeUglodon zone) : Shubuta, Mississippi (rare). 
Middle Jacksonian: Wilmington, North Carolina (very common); 3J miles 
south of Perry, Georgia (common) ; Rich Hill, 5-| miles southeast of Knoxville, 
Crawford County, Georgia (common) ; 18 miles west of Wrightsville, Johnson 
County, Georgia (common) ; 12 miles southeast of Marshallville, Georgia (com- 
mon) ; one-half mile southeast of Georgia Kaolin Company Mine, Twiggs County, 
Georgia (rare) ; Baldock, Barnwell County, South Carolina (rare). 
Lower Jacksonian (Moodys marl) : Jackson, Mississippi (rare). 
Cotypes. — Cat. Nos. 63905-63911, U.S.N.M. 
MEMBRANIPORIDRA SIMIL1S, new species. 
Plate 28, figs. 8-10. 
Description. — The zoarium incrusts other bryozoa and pebbles. The zooecia 
are elongated, little distinct, separated or not by a very little furrow, elliptical; 
the mural rim is thin at the top, enlarged below, finely granular. The opesium is 
