NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
841 
little or not salient, arranged in irregular quincunx. The mesopores are small, 
polygonal, numerous, closed by a calcareous lamella. The ovieell is very large, 
elliptical, as wide as the branches. 
Diameter of the peristome 0.14 mm. 
Diameter of the apertura 0.09 mm. 
Measurements. — . Dimensions of the ovieell 2.00 by 1.40 mm. 
Diameter of the mesopores 0.04 mm. 
Diameter of the branches 2.00-3.00 mm. 
V aviations. — The peristome is rarely visible. The zoarial cavities are com- 
pletely closed; they are often laterally constricted, preceded and followed by firm- 
atopores, their dimensions and their forms are absolutely irregular, and we have 
not yet discovered the reason for their formation. 
Affinities. — This species differs from Ascosoecia prominens in its hollow 
zoarium and in its club-shaped tubes. 
The ovieell is absolutely analogous to that of Cavea costata D'Orbigny, 1851, 
but the mesopores are irregularly disseminated and not grouped symmetrically 
on a double row between the peristomes. 
This species shows by the form of its ovieell that the generic distinction made 
by Gregory between Petalopora , Sparsicavea , and Cavaria is useless. 
Occurrence. — Midwayan (Clayton limestone) : Mabelvale, near Little Rock. 
Arkansas (very common) ; 1 mile west of Fort Gaines, Georgia (common). 
Cotypes.— Cat. No. 65262. U.S.N.M. 
Order CTENOSTOMATA Busk. 
Fossil representatives of this order of the Bryozoa are extremely rare com- 
pared with those of the other orders. In the Recent seas the Ctenostomata are 
likewise the least represented group of Bryozoa specifically, although some of the 
species are quite abundant and widespread. But a single form of this order has 
been discovered so far in the North American Early Tertiary rocks and it is too 
poorly preserved to merit description as a well-defined species. 
In the Ctenostomata the zooecia are usually isolated and developed by budding 
from the internodes of a distinct tubular stolon or stem. The orifice is terminal 
and has an operculum of setae. Marsupia are wanting. The zoarium is horny or 
membranaceous. 
All of the known Paleozoic Ctenostomata have been described by Ulrich and 
Bassler in their Revision of the Paleozoic Bryozoa. 1 Little study has been put 
upon the Mesozoic and Cenozoic forms but the Recent species have been the subject 
of numerous papers. 
1904. Ulrich and Bassler, Smithsonian Miscellaneous Collections, vol. 45, pp. 256-294, 4 pis. 
