20 BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 



Genus MEMBRANIPORA Blainville, 1834. 



(For description see Bulletin 106, U. S. National Museum, p. 77.) 



MEMBRANIPORA FLABELLATA Canu, 1904. 



Plate 10, figs. 10-14. 

 1904. Memhranipora ftabellala C.\nu, Les Bryozoaires du Patagonien echelle des Bryozoaires pour 



les terrains tcrtiares, Memoires Soci6t6 G6ologique de France, Paleontologie, vol. 12, p. 7, 



pi. 1. fig. 8. 

 1908. Membranipora flabellala Canu, Iconograpliie des Bryozoaires fossiles de I'Argentine, Anales 



del Museo Nacional de Buenos Aires, vol 17, p. 249, pi. 1, figs. 1-5. 



^ . fAo = 0.26 mm. „ . (Z2= 0.36-0.40 mm. 



Measurements. — Upesiai, _ ,„ Z,ooecia"|, rv oe _ 



^ llo=0.16mm. 1/2 =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. 



Vanations. — 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 AcantJiodesia 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 diff'ers in its smaller measurements (/io<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) : 2^ 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, T.S.X.M. 



MEMBRANIPORA FOSSULIFERA Ulrich and Bassler, 1904. 



Plate 9, figs. 6, 7. 

 1904. Menibranipora fossulifera Ulrich and Bassler, Brvozoa, Maryland Geological Survey 

 Miocene, p. 408, pi, 110, fig. 1. 



The original description is as follows: 

 Description.— Zo&fmm forming a thin expansion upon foreign bodies. Zooecia oblong, subquadrate, 

 sometimes obscurely hexagonal, arranged in regular longitudinal and diagonally intersecting rows', 

 i.vith about 11 in o mm., measuring lengthwise, 9 to 10 in 3 mm., diagonally, and 11 to 13 of the longi- 



