NORTH AMERICAN EARLY TERTIARY BRYOZOA. 305 



Genotype. Metracolposa robusta Canu and Bassler, 1917. Jacksonian. 



This genus differs from Cribrilina Gray, 1848, in its opercular dimorphir.ni. 

 Moreover, the operculum probably closes the ovicell during the whole period of 

 development of the embryo, as this is the habit in those species where the operculuia 

 closes the ovicell in opening. The ovicell occupies a large part of the distal 

 zooecia, the capacity of which is thus much reduced. The lumen pores are scarcely 

 visible, irregular, never prominent. 



METRACOLPOSA BREVIS. new species. 

 Plate 42, figs. 6, 7. 



Description. The zoarium is free, and bilamellar. The zooecia are large, ellip- 

 tical, short. The frontal is little convex; the costules are triangular, radial, seven 

 or eight pairs in number, separated by five or six lacunae concentrically arranged ; 

 no lumen pores. The aperture is transverse, semielliptical, bordered distally by a 

 very thin incomplete peristome. The ovicell is enormous, globular, smooth, opening 

 above the operculum but able to be closed by it. No avicularium. 



r7,.fl=0.14mm. . [3=0.80-0.90 mm. 



Measurements. Aperture^ 7 n no Zooecia{ , . ... . ._- 



1 7a=0.28 mm. 1 fe=0.60-0.70 mm. 



Affinities. This very elegant species may be distinguished from Metracolposa 

 grandis by its less length, greater width, the radial arrangement of the costules, 

 and the absence of avicularia. 



It differs from Metracolposa robusta in its greater width, its larger costules, 

 and the absence of avicularia. 



Occurrence. Middle Jacksonian: Near Lenuds Ferry, South Carolina (rare) ; 

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



Holotype.C&t. No. 64032, U.S.N.M. 



METRACOLPOSA GRANDIS, new species. 



Plate 42, figs. 8-13. 



Description. The zoarium is large, free, bilamellar. The zooecia are distinct, 

 elongated, large, elliptical. The frontal is convex; the costules are thick, nearly 

 transverse, little distinct, numbering from five to seven pairs and separated by 

 large circular lacunae. The aperture is transverse, semielliptical, bordered distally 

 by a very thin, incomplete, improminent peristome. The ovicell is very large, 

 elongated, prominent, globose, perforated by small irregular pores and decorated 

 in front by a large deltoid carina. A very large transverse oral avicularium above 

 each aperture. 



Measurements. Aperture f/>a=0.14-0.24 mm. Aperturef/ia=0.16 mm. 

 (ordinary) 1^=0.22-0.26 mm. (ovicelled) lZa=0.36 mm. 





 = 0.54-0.56 mm. 



55899 19 Bull. 106 - 20 



