320 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



is convex and formed of a tremocyst with small scattered pores; it is prolonged 

 into a long peristomie, smooth or a little granular ; the ascopore is large and salient. 

 The peristome is salient and it supports 2 to 5 small avicularia with pivot; the 

 peristomice is elliptical, transverse, oblique. 



( hpe=0.10 mm. . [Zs=0.75-0.80mm. 



Measurements. Feristomice {, /ooecia 7 nAn nKn 



[lpe=0.20mm. [{2=0.40-0.50 mm. 



Variations. The diagrammatic section (fig. 6) illustrates the structure of this 

 species; the small peristomial avicularia are visible as small cavities. 



The ascopore is perfectly visible in the interior (fig. 10). It opens manifestly 

 into the zooecium below the operculum. The frontal is formed of a tremocyst with 

 tubules placed on a very thin perforated olocyst; these tubules have thick walls; 

 it is difficult to see them on the transverse sections (fig. 9). 



The longitudinal thin section is very curious (fig. 12). It shows on the median 

 axis a series of fusiform zooecia disposed in chaplet, the latter resulting fiom the 

 alternation of zooecia as seen in perspective. 



Affinities. This species is much larger than Acropora coronata Reuss, 1847; the 

 zooecia are more distinct ; the peristomial avicularia are smaller. 



It differs from Gastropella asperula in its frontal with numerous tremopores 

 and in the absence of areolae. 



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

 mile north of Monroeville, Alabama (very common). 



Vicksburgian (Red Bluff clay) : Seven and one-half miles southeast of Bladon 

 Springs, Alabama (very rare). 



Cotypes.Cat. No.' 64263, TJ.S.N.M. 



Genus GASTROPELLA Canu and Bassler, 1917. 



1017. Gastropclla OANU aud BASSLER, Synopsis of American Early Tertiary Oheilostome 

 Bryozoa, Bulletin 96, United States National Museum, p. 37. 



An Acropora having a smooth frontal garnished laterally with areolae. 

 Genotype. Gastropella ventricosa Canu and Bassler, 1917. 

 Range. Midwayan : Jacksonian. 



GASTROPELLA VENTRICOSA Canu and Bassler, 1917. 



Plate 6, figs. 7-12. 



1917. Gastropclla ventricosa CANU and BASSLER, Synopsis American Early Tertiary Cheilos- 

 tome Bryozoa, Bulletin 96, United States National Museum, p. 38, pi. 4, fig. 3. 



Description. -The zoarium is free, cylindrical, bifurcated. The zooecia are 

 large, elliptical, swollen; the frontal is smooth, convex, garnished laterally with 

 some large areolae. The ascopore is very large, not salient, placed in the upper 

 third of the zooecia. The peristome is salient and sharp; the peristomice is oblique, 

 orbicular or elliptical. The ovicell is entirely hidden within the thickness of the 

 frontal of the distal zooecium. 



