NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
447 
Variations . — The rimule-spiramen is unsymmetrical and oblique; it is formed 
of two lateral lips not arranged on the same plane; one is always higher than the 
other; the lower is alwa} T s adjacent to the large avicularium. When the two oral 
avicularia are symmetrical the rimule is symmetrical. There is, therefore, a certain 
relation between the functions of the avicularia and the hydrostatic system. The 
longitudinal section shows a very large ovicell opening into the peristomie above 
the operculum, and a large septula (multiporous) at the base of the zooecia (fig. 10). 
The tangential section (fig. 8) shows the structure of the frontal, which is a 
tremocyst with tubules. The convexity of the zooecia allows one to note the sub- 
jacent olocyst at the edge of the tremocyst (fig. 9). 
Affinities . — In the interior the apertura bears a proximal spine forming a sort 
of lyrula (fig. 7) which disappears easily in fossilization. This species differs 
from M etradolium sulciferum in its smaller tremopores not arranged at the base 
of the sulci. 
It differs from M etradolium dissimile in the general absence of zooecia with a 
spiramen and in the lesser width of the peristomice (lpe=0.15 and not 0.20 mm.). 
Occurrence . — Middle Jacksonian: Wilmington, North Carolina (very com- 
mon) ; 3J miles north of Grovania, Georgia (rare) ; 12 miles southeast of Marshall- 
ville, Georgia (common) ; Rich Hill, Crawford County, Georgia (very common) ; 
18 miles west of Wrightsville, Georgia (rare) ; 3^ miles south of Perry, Georgia 
(common) ; near Lenuds Ferry, South Carolina (very common). 
Cotypes. — Cat. No. 64121, U.S.N.M. 
METRADOLIUM SULCIFERUM, new species. 
Plate 14, figs. 5-15. 
Description . — The zoarium is free, bilamellar, erect; the fronds are com- 
pressed, narrow, bifurcated. The zooecia are large, elongated, indistinct; the 
frontal is convex, thick, formed of a tremocyst with tubules, supported by a very 
thin olocyst, finely perforated with corresponding pores and closely joined. The 
apertura is formed of a semilunar anter and of a concave poster supporting a very 
short median lyrula; the peristomice is oblique and is formed of an anter with 
undefined outlines and an unsymmetrical rimule-spiramen. There are two avicu- 
laria symmetrically placed on each side of the rimule ; the larger is provided with 
a pivot and with a very large mandible. 
Measurements . — Aperture 
(interior) 
la— 0.12 mm. 
Zooecia 
\Lz= 1.00-1.25 mm. 
\lz= 0.30-0.40 mm. 
Variations . — On the young fronds (figs. 6, 12) the median zooecia are unpro- 
vided with oral avicularia; the lateral zooecia bear only large avicularia. In the 
normal zooecia, there are two avicularia; the larger is adjacent to the lower lip of 
the rimule (fig. 8). In the old zooecia the large avicularium is lost among the 
tubules and opens then into the peristomie (figs. 9, 10, 11). The more the tubules 
