NORTH AMERICAN EARLY TERTIARY BRYOZOA. 121 



avicularia are interopi-sial. very small, elliptical, little raised. The aneestrnla is 

 very small. 



. lho-0.24r-0.30 mm. . (2= 0.40 mm. 



M, itxiuYmi'iits. Opesia Zooecia , 



1/0=0.16-0.18 mm. |fe=0.24 nun. 



Variations. A remarkable phenomenon in this species is the d!/>t-or/i/i!xi of 

 the mural rim. On the same zoariuin, without any apparent reason, there are 

 mural rims thin and distinct, and others thick and confluent. The first are devoid 

 of dietellae while the second have five of them. These small pore-chambers are 

 not therefore indispensable to the life of all the zooecia of the same zoarium, and 

 not even to the passage of the mesenchymatous fibers. The ancestrula is very 

 small. Around it the zooecia have always a separate mural rim and are not 

 always accompanied by avicularia. The same holds true on the zoarial margins. 

 We have not observed regenerated zooecia. 



Affinities. This species differs from Membrendoetium rectum, in its confluent 

 mural rims not enlarged at the base and in its very inconspicuous avicularia. The 

 specimen figured from Bainbridge. Georgia, is altered chemically, as are most of 

 the specimens from this locality. 



Occurrence. Upper Jacksonian (Ocala limestone) : Bainbridge, Georgia; Red 

 Bluff, on Flint River, 7 miles above Bainbridge, Georgia (rare) ; west bank of 

 Sepulga River, Escambia County, Alabama (rare) ; Chipola River, east of Mari- 

 anna, Jackson County, Florida (rare). 



Middle Jacksonian: Baldock, Barnwell County, South Carolina (rare): 18 

 miles west of Wrightsville, Johnson County, Georgia (very rare). 



Lower Jacksonian (Moodysmarl) : Jackson. Mississippi (very rare). 



Cotypes.Cat. Nos. 63889-63892, U.S.N.M. 



MEMBRENDOECIUM LOWEI, new species. 



Plate 81, fig. 1.. 



Description. The zoarium incrusts small pebbles, from which it becomes easily 

 detached. The zooecia are elongated, elliptical, distinct, or confluent: the mural 

 rim is broad, flat, granulose. The opesium is elliptical or oval, the narrow end 

 proximal. The ovicell is a very small, distal convexity. The avicularia are very 

 indistinct and not prominent. 



,, . \ho~0.20 mm. . \Lz = O.SO mm. 



Measurements. Opesia , . Zooecia , 



1/0=0.12 mm. \h =0.20-0.22 mm. 



Affinities. The mural rims are very often united, so that the boundary between 

 the zooecia is little visible. It is impossible to say whether the avicularia are 

 indeed present or if these are only interopesial cavities. If, therefore, our observa- 

 tion of the endozooecial ovicells should not be confirmed, it would be necessary to 

 place this species under Conopeum. 



Memlircndoccium loivei differs from M. chipJe.v in its smaller micrometric 

 dimensions and in its inconspicuous avicularia. 



