94 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Variations and affinities . — Like Conopeum lamellosum , this species presents on 
its zoarial surface subcolonies which do not originate from a larva, but instead 
from the especial proliferation of a subjacent zooecium (fig. 12). These develop 
chief!}" at the bifurcations of the algae, which are the parts most constant and least 
susceptible to growth which might disorganize the zoarium. In tangential thin 
sections the interopesial cavities have special walls (fig. 16). On the inner face of 
the zoarium the zooecia .are elliptical and provided with a distal collar (fig. 14). 
The mural rims are adjacent, but may be sometimes separated by a very small 
furrow. The marginal zooecia are deformed wherever the subcolonies meet. On 
certain zoaria there are some zooecia bearing a kind of gymnocyst rather well devel- 
oped ; again the interopesial cavities sometimes have the form of prominent and 
pointed avicularia. 
This is a good-sized fossil, and its large zoarial dimensions will aid in its 
determination even in the field. 
Conopeum arborescens differs from C. lamellosum in the form of its zoarium, 
in the oval shape of the opesium, in the rarity of furrdws separating the zooecia, 
and in the greater thickness of the mural rim. 
Occurrence . — Lower Jacksonian (Moodys marl) : Jackson, Mississippi (com- 
mon) ; 2f miles north of Robert, Mississippi (common). 
Cotypes. — Cat, No. 63873, U.S.N.M. 
Genus HELIODOMA Calvet, 1907. 
1907. Heliodoma Cat.vet, Bryozoaires Expedition Scientifique du Travailleur et du Talis- 
man, p. 396. 
The zooecia, with frontal provided with a membraneous area, are arranged 
following two concentric spiral series in which they alternate, separated by a spiral 
series of vibracula (Calvet). 
Genotype. — Heliodoma implicate Calvet. 1907. Recent, 
The two genera Cupuladria and Heliodoma differ only in the place of the 
vibracula. They can be maintained only if it is proved that the function of the 
vibraculum is different in them. The name of Heliodoma would then have the 
right of priority. 
Genus MEMBRANIPORINA Levinsen, 1909. 
1909. Memhraniporina Levinsen, Morphological and Systematic Studies on the Cheilostoma- 
tous Bryozoa, p. 145. 
Membranipores exhibiting neither ovicells nor avicularia. 
Memhraniporina is not a true genus, but is simply an artificial grouping pro- 
posed by Levinsen for the reception of species incompletely described or of which 
we have insufficient information to place them more definitely. 
MEMBRANIPORINA RIMULATA Ulrich, 1901. 
Plate 1, figs. 1, 2. 
1901. Membranipora rimulata Ulrich, Maryland Geological Survey, Eocene, p. 211, pi. 60. 
figs. 1, 2. 
Original description . — “ Zoarium adnate, forming a thin, single sheet of 
indefinite extent. Zooecia hexagonal in form, arranged quincuncially, with the Ion- 
