24 BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 



Variations. — Our niicromctric measurements have been made as far as possible 

 from the ancestrula on our single specimen. The opesium of the small ancestrular 

 zooecia measures onh- 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.—€i\t. 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 tliin, rounded, very 

 finely crenulated, salient, ornamented with two distal tubercles; the proximal 

 cryptocyst is concave and very small. The opesium is elliptical. 



,, . r\ ■ f ^0 = 0.30 mm. „ . fZ2 = 0.35mm. 



Measurements. — Opesia \ ^ „ ^^ Zooecia \ ^ „ ^„ 



^ vlo = 0.20 mm. I iz = 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 cryptocj-st placed 

 only in the proximal portion of the zooecium, by its larger micrometric measurements 

 (Z/0 = O.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 tendla Hincks, Contributions History Marine Polyzoa, Foreign Membrani- 

 porina II, .\nnals Magazine Natural History, ser. 5, vol. 6, p. 376, pi. 16, fig. 7. 



1889. Membranipora tenella Jelly, SjTionyniic catalogue of recent marine Bryozoa, p. 167. 



1919. Cqllopora tenella Canu and Bassler, Geology and Paleontology of the West Indies, Bryozoa, 

 Publication of the Carnegie Institution at Washington, No. 291, p. 81, pt. 5, fi". 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. 



