138 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



regularly elliptical, very finely crenulated. The primoserial zooecia are modified. 

 The ovicell is large, distinct from the mural rim, salient, globular, almost trans- 

 verse, and is deeply embedded in the distal zooecium. 



Measurements. Opesia 



Ao=0.36-0.44 mm. 7 . (3=0.50-0.60 mm. 



Zo=0.20-0.30 mm. ia |Zs=0.30-0.40 mm. 



Affinities. We have chosen for illustration specimens showing the most con- 

 stant features, but the variations are numerous. The least roughness of the 

 substratum modifies the micrometric dimensions very much. 



The primoserial zooecia have no decided form and they sometimes assume the 

 shape of large interzooecial avicularia. A zoarium from Old Factory near Bain- 

 bridge, Georgia, covers four square centimeters. The distal septula is rather large, 

 but it is only easily visible after abrasion of the surface. 



This species resembles Membraniporidra spissimiiralis very much, but it differs 

 in the absence of a cryptocyst with lateral grooves and in the smaller micrometric 

 dimensions (Zs=0.60 mm.), 



Occurrence Middle Jacksonian: Near Lenuds Ferry, South Carolina (com- 

 mon) ; Eutaw Springs, South Carolina (very rare). 



Upper Jacksonian (Ocala limestone) : Old Factory, 1| miles above Bainbridge, 

 Georgia (rare). 



'Vicksburgian ("Chimney rock" of Marianna limestone) : One mile north of 

 Monroeville, Alabama (rare) ; Vicksburg, Mississippi (very rare in the lower beds). 



Cotypes.Cat. No. 63912, U.S.N.M. 



MEMBRANIPORIDRA PYRIFORMIS, new species. 

 Plate 28, figs. 11-13. 



Description. The zoarium incrusts oyster shells and pebbles. The zooecia are 

 elongate, distinct, pyriform, with or without a small gymnocyst; the mural rim is 

 thick, curved, salient, broader below. The opesium is entire, pyriform and anterior. 

 The ovicell is a little distal embedded niche covered bv a slightly salient convexity. 



Measurements. Opesia 



A0=0.35-0.40 mm. . |Zs=0.50-0.55 mm. 



0=0.25-0.30 mm. ia |te=0.45-0.50 mm. 



Affinities. The very small ovicell is often difficult to discover on specimens a 

 little altered by fossilization. It is hyperstomial, that is to say. buried in the distal 

 zooecium, but it is so embedded that it can not be considered as endozooecial. Every- 

 where it opens into the interior of the zooecium below the opercular valve. 



This species has somewhat the aspect of Membranipora appendiculata Eeuss, 

 1847, but differs from it in the absence of avicularia. 



Occurrence. Upper Jacksonian (Ocala limestone) : Old Factory, H miles 

 above Bainbridge. Georgia (common) ; Red Bluff. 7 miles above Bainbridge, 

 Georgia (very rare), Bainbridge, Georgia (rare) ; Chipola River, east of Marianna, 

 Jackson County, Florida (very rare) ; west bank of Sepulga River, Escambia 

 County, Alabama (common). 



Cotypes.Cnt. Nos. 63915, 63916, U.S.N.M. 



