24 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
Variations. —Our micrometric measurements have been made as far as possible 
from the ancestrula on our single specimen. The opesium of the small ancestrular 
zooecia measures only 0.30 by 0.20 mm. The number and size of the tubercles is 
very irregular. They are hollow. 
This species differs from Membranipora osburni in its larger dimensions, and in 
the presence of two pairs of lateral tuberosities. 
Occurrence. —Miocene (St. Mary’s formation): Cove Point, Maryland (very 
rare). 
Holotype. —Cat. No. 68408, U.S.N.M. 
MEMBRANIPORA OSBURNI, new species. 
Plate 46, figs. 11, 12. 
Description .—The zoarium incrusts sponges. The zooecia are distinct, sepa¬ 
rated by a furrow, elongated hexagonal; the mural rim is thin, rounded, very 
finely crenulated, salient, ornamented with two distal tubercles; the proximal 
cryptocyst is concave and very small. The opesium is elliptical. 
,, . ~ [Ao = 0.30mm. „ . f Iz = 0.35 mm. 
Measurements .—Opesia \ , _ __ Zooecia 1 7 „ „ 
r l lo =0.20 mm. I tz =0.28 mm. 
Affinities .—The micrometric measurements are smaller than Membranipora 
vaughani, but the species is quite close to Membranipora tuberculata Busk, 1859, in 
its two distal tubercles. It is distinguished from the latter by its cryptocyst placed 
only in the proximal portion of the zooecium, by its larger micrometric measurements 
(Z 2 = 0.35 mm. and not 0.30 mm.), and in its much thinner mural rim. 
We dedicate this interesting species to Dr. Raymond C. Osburn, of the Ohio 
State University, in honor of his important researches upon American recent 
bryozoa. 
Occurrence. —Pleistocene: Mount Hope, Panama Canal Zone (rare). Miocene 
(Bowden marl): Bowden, Jamaica (rare). 
Holotype. —Cat. No. 68409, U.S.N.M. 
Group MEMBRANIPORAE Canu and Bassler, 1917. 
SECTION I. NO OVICELL. 
Genus MEMBRANIPORINA Levinsen, 1909. 
(For description see Bulletin 106, U. S. National Museum, p. 94.) 
MEMBRANIPORINA TENELLA Hincks, 1880. 
Plate 5, figs. 10, 11. 
1880. Membranipora tenella Hincks, Contributions History Marine Polyzoa, Foreign Membrani- 
porina II, Annals Magazine Natural History, ser. 5, vol. 6, p. 376, pi. 16, fig. 7. 
1889. Membranipora tenella Jelly, Synonymic catalogue of recent marine Bryozoa, p. 167. 
1919. Callopora tenella Canu and Bassler, Gfeology and Paleontology of the West Indies, Bryozoa, 
Publication of the Carnegie Institution at Washington, No. 291, p. 81, pt. 5, fig. 10. 
Affinities .—This species is quite easily recognized by its very thin mural rim 
and especially by its small tubercles arranged more or less symmetrically on the 
gymnocyst. These tubercles appear to be hollow. 
