NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
305 
Genotype. — M etracolposa robusta Canu and Bassler, 1917. Jacksonian. 
This genus differs from Cribrilina Gray, 1818, in its opercular dimorphism. 
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 operculum 
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. 
Measurements . — Aperture 
ha— 0.14 mm. 
la= 0.28 mm. 
Zooecia 
Lz= 0.80-0.90 mm. 
73=0.60-0.70 mm. 
Affinities .— This very elegant species may be distinguished from M etracolposa 
grandis by its less length, greater width, the radial arrangement of the costules, 
and the absence of avicularia. 
It differs from M etracolposa robusta in its greater width, its larger costules, 
and the absence of avicularia. 
Occurrence .- — Middle Jacksonian: Near Lenucls Ferry, South Carolina (rare) ; 
18 miles west of Wrightsville, Johnson County, Georgia (rare). 
Holotype. — Cat. 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 7^=0.14-0.24 mm. 
(ordinary) IA?= 0.22-0. 26 nun. 
„ . fZs=0.90-1.10 mm. 
Zooecia; 7 A „ . n 
I fe= 0.54-0,56 mm. 
Aperture) ha= 0.16 mm. 
'ovicelled) \Za=0.36 mm. 
55S99— 19— Bull. 106 20 
