NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
381 
This is truly an American genus and it furnishes us with many important 
stratigraphic data, as noted in the table below : 
Geological distribution , species of Hippomenella. 
Hippomenella rotula, new species 
Hippomenella transversata, new species 
Hippomenella angustaedes , new species. 
Hippomenelle inconiita, new species . . . 
Hippomenella capitimortis , new species. 
Hippomenella costulata, new species 
Hippomenella alifera , new species 
Hippomenella radicata, new species 
Hippomenella transversora, new species 
Hippomenella pungens, new species 
Hippomenella punctata, new species 
Hippomenella ligulata, new species 
Hippomenella tuberosa, new species 
Hippomenella axiculata, new species. . . 
Hippomenella crassicollis, new species.. 
Lower 
Middle 
Jackson- 
Jackson- 
ian. 
ian. 
+ + 
+ + 
+ ■ + 
Upper 
Jackson- 
ian. 
Vicks- 
burgian. 
+ 
+ 
Thus the lower Jacksonian is characterized by Hippomenella rotula alone; the 
middle Jacksonian by Hippomenella transversata , H. angustaedes , H. ligulata , H. 
axiculata , and H. tuberosa ; the upper Jacksonian by no species. The Vicksburgian 
is characterized by 11. capitimortis , 11. costulata, 11. transversora and 11. pungens. 
H. radicata , and H. alifera range through the entire Jacksonian. 
Group 1. ZOAEJUM BILAMELLAK. 
HIPPOMENELLA ROTULA, new species. 
Plate 49, figs. 4-14. 
Description. — The zoarium is free, formed by two lamellae, back to back, and 
inseparable. The fronds are flat or undulating and may measure 2 centimeters in 
length. The zooecia are distinct, very elongated, fusiform ; the frontal, little con- 
vex and smooth, is garnished laterally with a double row of areolae much crowded. 
The aperture is elliptical (in the interior) ; it presents exteriorly a mucronoicl 
convexity very salient on its proximal border; there are two very small cardelles. 
The ovicell is large, globular, salient, much imbedded in the distal zooecia ; the 
two lateral areas bear three of four large cavities separated by radial projections. 
The avicularia are small, inconstant, placed laterally below the aperture, provided 
with a pivot, and with a triangular beak directed toward the base. No spines. 
Measurements. — Aperture f/ia=0.lT mm. „ . fZs=0.60-1.00mm. 
(interior) \la— 0.15 mm. ooccia, 0.40-0.50 mm. 
Variations. — The micrometric variations are extraordinary; they vary from 
one to two times. There are sometimes narrow zooecia (fig. 5), again there are 
wide zooecia (fig. 6), and often giant zooecia (fig. 7). The avicularia are' absent 
(fig. 5) or present (figs. 7-9), generally small. The mucronoid convexity is promi- 
nent (fig. 5) or absent (fig. 7). The cavities and the pores of the ovicell are 
variable in size and in position (figs. 7, 8). 
