NORTH AMERICAN EARLY TERTIARY BRYOZOA. 255 



base. The cryptocyst is deep, smooth, and somewhat convex ; the polypidian con- 

 vexity is improminent and the opesiules somewhat linear. The ovicell is globular, 

 salient, smooth, opening in a large orifice above the opercnlar valve. The avicularium 

 is interzooecial, smaller than the zooecium, fusiform, terminated by a small but wide 

 canal; its opesium is median and very small. 



f 7(0=0.10 mm. . , . \Lav= 0.40-0.50 mm. 



Measurements. Opesium , Aviculariunvi 7 



[lo=0.1o mm. (lav=0.2Q mm. 



Zooe.cium js=0.55-0.60 mm. 

 (including opesiules) \lz= 0.35-0.40 mm. 



Affinities. This species differs from Aechmella filimargo in its hyperstomial 

 ovicell. It may be distinguished from BJiagasostoma minusculum by its larger 

 dimensions. Specimens from both the Jacksonian and Vicksburgian have been 

 discovered. It appears to us that there were no essential differences between them, 

 so we have united them under the same species. 



Occurrence. Middle Jacksonian (Castle Hayne limestone) : Wilmington, North 

 Carolina (very rare). 



Vicksburgian (Marianna limestone) : Salt Mountain, 5 miles south of Jackson, 

 Alabama (very rare). 



Cotypes. Cat. Nos. 64000, 64001, U.S.N.M. 



RHAGASOSTOMA MINUSCULUM, new species. 

 Plate 39, fig. 8. 



Description. The zoarium incrusts bryozoa. The zooecia are very small, oval, 

 distinct, separated by a furrow; the mural rim is prominent, slightly thickened, 

 enlarged at the base, complete. The cryptocyst is deep, smooth, flat ; the polypidian 

 convexity is improminent; the opesiules are rounded incisions. The ovicell is 

 globular and prominent. The avicularium is interzooecial, elongated, fusiform, ter- 

 minated by a very short but wide canal. 



f/w=0.07mm. . fZai>=0.20mm. 



Measurements. Opesium , -..- Avicularmm , 



U0=0.10mm. Ua?'=0.10mm. 



Zooecium [Zs=0.30-0.35 mm. 

 (including opesiules) 1/3=0.24-0.28 mm. 



Affinities. This is one of the smallest bryozoans known. It is difficult to con- 

 ceive how such a small structure could contain tentacles, pharynx, stomach, intes- 

 tines, muscles, and ovaries and lodge a creature much more perfected than an oyster 

 or a Tridacne. 



Occurrence. Middle Jacksonian: Wilmington, North Carolina (very rare); 

 Eutaw Springs, South Carolina (very rare). 



Holotype.Cat. No. 64002, U.S.N.M. 



