20 
BULLETIN" 125, UNITED STATES NATIONAL MUSEUM. 
Genus MEMBRANIPORA Blainville, 1834. 
(For description see Bulletin 106, U. S. National Museum, p. 77.) 
MEMBRANIPOKA FLABELLATA Canu, 1904. 
Plate 10, figs. 10-14. 
1904. Membranipora Jlabellala Canu, Les Brvozoaires du Patagonien echelle des Bryozoaires pour 
les terrains tertiares, Memoires Society Gdologique de France, Paleontologie, vol. 12, p. 7, 
pi. 1, fig. 8. 
1908. Membranipora flabellata Canu, Iconographie des Bryozoaires fossiles de l’Argentine, Anales 
del Museo Nacional de Buenos Aires, vol 17, p. 249, pi. 1, figs. 1-5. 
,, , „ \ho = 0.26 mm. ,, . \Lz — 0.36-0.40 mm. 
Measurements. —Opesiaj, Zooeciau nn „ 
1 llo =0.16 mm. U 2 =0.26 mm. 
Structure. —The zoarium incrusts shells and algae over large surfaces forming 
many superposed lamellae. The tubercles of the interzooecial angles are well pre¬ 
served only on the inner lamellae, the outermost lamellae being deprived of them. 
The zooecia are very deep, the mural rim is quite thick, and the opesium is crenu- 
lated. The superior lamellae are formed of zooecia developed around pseudoan- 
cestrulae. The latter do not arise from the development of a larva, but they are 
produced by the gemmation of an inferior zooecium. 
Variations. —One of our species from Yorktown, Virginia, is exactly similar to 
the typical Argentina specimens, but our other examples present variations not 
noted in the types. The variations are due evidently to the diversity of conditions 
under which the species existed, as its geographic distribution appears very great. 
The tubercles are very inconstant (fig. 10) and entire colonies are deprived of 
them (fig. 12). The young zooecia have thin mural rims (fig. 12) which gives them 
an aspect similar to that of Acanthodesia savarti Audouin, 1826, but old zooecia 
are normal and there are never large zooecia giving rise to new rows. Sometimes 
the two distal tubercles are joined together (fig. 13). The tubercles are often 
replaced by interopesial cavities (fig. 11) on the much expanded zoaria, but the 
presence of normal tuberose zooecia reveals the true nature of these sorts of 
specimens. 
Affinities. —The exterior aspect much recalls Acanthodesia oblongula Ulrich and 
Bassler, 1904, but the present species differs in its smaller measurements (ho<0.30 
mm.) in the absence of opesial spicules and in its multilamellar colonies. 
Occurrence. —Miocene (Yorktown formation): Yorktown, Bellfield and Suffolk, 
Virginia (rare). Miocene (Duplin marl): 2h miles northwest of Chocowinity and at 
Snow Hill, North Carolina (rare). 
Geological distribution.— Patagonian, Pampean and Post Pampean of Argen¬ 
tina (Canu). 
Plesiotype. —Cat. Nos. 68401, 68402, U.S.N.M. 
MEMBRANIPORA FOSSULIFERA Ulrich and Bassler, 1904. 
Plate 9, figs* 6, 7. 
1904. Membranipora fossulifera Ulrich and Bassler, Bryozoa, Maryland Geological Survey, 
Miocene, p. 408, pi. 110, fig. 1. 
The original description is as follows: 
Description. —Zoarium forming a thin expansion upon foreign bodies. Zooecia oblong, subquadrate, 
sometimes obscurely hexagonal, arranged in regular longitudinal and diagonally intersecting rows, 
with about 11 in 5 mm., measuring lengthwise, 9 to 10 in 3 mm., diagonally, and 11 to 13 of the longi- 
