308 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Variations. — The distal avicularia are inconstant; they are sometimes atten- 
uated (fig. 16) and even absent (fig. 18). 
The keel of the ovicell, very clear in figure 17, is much attenuated in figure 15. 
We have observed (fig. 17) an aperture closed by a calcareous operculum. 
This phenomenon is frequent in all the Cheilostomes, but as yet zoologists have not 
learned its significance. 
Certain zoaria are narrow at their lower extremity (fig. 18) as if they were 
formed of segments for articulation. The base of such segments (fig. 20) bears 
three pores, which is not the case in articulated zoaria. 
The zooecial walls (fig. 19) are very thin. The ovicell occupies a portion of 
the cavity of the distal zooecia. As in the other species of the same genus the 
costules are apparently not hollow. 
Affinities. — This species is distinguished from all others of the genus by its 
cylindrical zoarium, but it is very close to Metracolposa robusta of which it might 
be a variety if we had intermediate forms. It differs from the latter in having a 
larger number of costules, in the presence of two larger distal avicularia and in 
the smaller zooecial breadth, and from Metracolposa grandis in its much smaller 
lacunae and its very different micrometrical dimensions. 
Occurrence. — Middle Jacksonian: Wilmington, North Carolina (common); 
near Lenuds Ferry, South Carolina (very common). 
Cotypes. — Cat. No. 64034, U.S.N.M. 
Genus CORBULIPORA MacGillivray, 1895. 
1S95. Corbulipora MacGillivray, Monograph Tertiary Polyzoa Victoria, Transactions Royal 
Society Victoria, vol. 4, p. 60. 
“Zoarium erect, zooecia quadriserial, facing to the four sides, much elongated, 
calcareous, readily separating longitudinally. Anterior part wider, raised, formed 
by a series of vertical ribs on each side, turning abruptly inwards and uniting to 
form a flat plate; posterior part of zooecia narrow, smooth, and entire; thyrostome 
with the upper lip arched, thickened and smooth.” (MacGillivray.) 
Genotype. — Corbulipora ornata MacGillivray, 1895. 
Range. — Eocene-Miocene. 
This genus is purely zoarial. The figures given by MacGillivray are incom- 
plete. Two specimens that have been sent to us by Mr. Maplestone are somewhat 
different from MacGillivray’s description. The costules have lumen pores; the 
initial slit separating two costules is very small. The genus has the costular struc- 
ture of Gephyrotes. 
CORBULIPORA COLLARIS, new species. 
Plate 43, fig. 14. 
D escription. — The zoarium is free, quadriserial, bifurcated. The zooecia are 
distinct, separated bv a prominent, thread or a furrow, and are much elongated, 
elliptical; the frontal is convex; the costules are fine, numerous, ornamented with 
very small lumen pores; separated by a large, initial slit, followed by two lacunae; 
the superior costules are more or less united to form a sort of collar. The aperture 
