NORTH AMERICAN EARLY TERTIARY BRYOZOA. 363 



frontal is little convex and formed by a tremocyst with numerous wide open pores. 

 The aperture is oval, with a wide, rounded rimule, separated from the anter by 

 two condyles visible in the interior. The ovicell is large, globular, salient: it 

 completely surrounds the aperture, forming around it a prominent peristomie; 

 it is formed of a large frontal area surrounded by a salient collar. The median 

 avicularium is long, very thin, remote from the aperture. 



,, f Aa=0.12-0.14 mm. . fZs=0.60-0.70mm 



Measurements Aperture Zooecia] 7 ft Kn 



[Za=0.12-0.14 mm. [?2=0.50mm. 



Variations. The beak of the avicularium is very long, thin, and fragile ; it 

 is only visible on the best preserved specimens (fig. 11) ; on others it has the aspect 

 of a small triangular pore (fig. 8), but always remote from the aperture and not 

 salient. 



The zooecia with a thick tremocyst are sometimes bordered by a small salient 

 thread (fig. 8). 



The frontal area of the ovicell is fragile ; it often disappears in the process of 

 fossilization. 



The orifice of the ovicelled zooecia is quite variable. The operation of the 

 operculum appears to be complex. It must be lowered much externally to permit 

 the extrusion of the tentacles, which ought, moreover, to be very thin. The oper- 

 culum never closes the ovicell because the outer orifice does not exactly correspond 

 to its form, but in opening it offer a shelter sufficient for the passage of the eggs. 

 It is probable also, as in many other Schizoporeltae that it remains closed during 

 the escape of the larvae. 



In figure 8 the reader may note two zooecia which are transformed into inter- 

 zooecial avicularia analogous to the zooecia of Arthropoma cecilii Savigny-Audouin, 

 1812-1826, figured in 1890 by Kirkpatrick and which we have reproduced on text 

 figure 105. 



We have observed (fig. 8) a calcified zooecium whose aperture is covered by 

 the tremocyst. 



The median avicularium is the result of the development of an inner bud, 

 as it is easy to note on inner surfaces. 



Affinities. -This species differs from Metroperiella biplanata, in which zoarium 

 is also bilamellar, in its much larger instead of very minute tremopores. 



It differs from Metroperiella grandipora in its smaller aperture (Za=0.12 mm. 

 instead of 0.15 mm), its median avicularium, which is very large and remote from 

 the aperture, and its zoarium, which is bilamellar and not pleurilamellar. 



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

 mon) ; Wilmington, North Carolina (common) ; 3J miles south of Perry, Georgia 

 (rare). 



Cotypes.Cnt. No. 64066, U.S.N.M. 



