NORTH AMERICAN EARLY TERTIARY BRYOZOA. 471 



frontal is convex and surrounded by a line of areolae; it is formed of a smooth 

 olocyst, perforated laterally, surmounted by a smooth or porous pleurocyst. The 

 peristome is salient, thin, sharp; the peristomice is elongated and elliptical; the 

 apertura is semilunar with a very concave proximal border; the lyrula is quite 

 small and very fragile. The ovicell is hyperstomial and placed on the distal zooecia 

 but is little salient ; it is widely open in the peristomie. The median avicularium is 

 small, orbicular, with a fragile pivot. 



Measurements.-Peristomice J ? 7 >pe = mm ' Apertura [ * a= 



[tpe=Q.15mm. u=0.1omm. 



ry (Zs=O.SO-0.!)Omm. 

 Zooecia 



[?3=0.35 mm. 



Variations. The aspect of this species is quite variable; the most habitual 

 (figs. 2, 3) shows a pleurocyst with much scattered pores. But on the younger 

 zooecia (fig. 4) the pleurocyst is smooth and there is a line of areolae around 

 each zooecium. The zooecia are sometimes separated by a salient thread on speci- 

 mens strongly calcified (fig. 6). 



On the plurilamellar zoaria the zooecia are irregularly oriented and often 

 wider (fig. 7). The transversal sections show that the zooecia are provided with 

 a very thick frontal (figs. 9, 11). 



Affinities. This species differs from Smittina pupa in the presence of a small 

 median avicularium and the absence of lateral avicularia. Under the microscope 

 the distinction is often very difficult. 



Certain small specimens of Smittina angulata Reuss, 1866, resemble this 

 species and their differentiation is difficult for the two species are quite variable. 

 Smittina tubulata is deprived of lateral avicularia and the zooecia are longer. 



The size of the zoarium makes this an easily recognized fossil. 



Occurrence. Vicksburgian (" Chimney rock " of Marianna limestone) : One 

 mile north of Monroeville, Alabama (very common). 



Vicksburgian (Red Bluff clay) : Seven and one-half miles southwest of Bladen 

 Springs, Alabama (rare). 



Plesiotypes.C&t. No. 64302, U.S.N.M. 



Genus PLAGIOSMITTIA Canu and Bassler, 1917. 



1917. Plagiosmittia CANU and BASSI.EE, Synopsis of American Early Tertiary Cheilos-tome 

 Bryozoa, Bulletin 9ti, United States National Museum, p. 51. 



The ovicell opens into the peristomie. The frontal is a tremocyst. The 

 avicularium is placed in the peristomie. The zooecia are oriented transversally to 

 the zoarial fronds. Two large condyles are placed in the interior back of the 

 apertura; they limit a small canal leading to the orifice of the compensatrix. 



Genotype. Plagiosmittia regularis Canu and Bassler, 1917. 



Range. Jacksonian-Vicksburgian. 



This genus differs little from Pordla Gray, 1848, in the nature of its func- 

 tions. The difference lies in the irregularity of the place of the median avicularium 



