NORTH AMERICAN EARLY TERTIARY BRYOZOA. 769 



PLEURONEA ALVEOLATA, new species. 



Plate 107, figs. 10-18. 



Description. The zoarium is free, arborescent, bifurcated, idmoneiform with 

 subcircular section. The fascicles are salient, opposite, crowded, and formed of 

 five or six tubes at the maximum. The tubes have their upper portion visible and 

 are separated by a salient line; the peristome is thin and rectangular. The basal 

 lamella is ornamented with large tergopores with orifices more or less funnel- 

 shaped, giving them the aspect of alveolae. 



(Diameter of the peristome__ _ 0.12 mm. 



M, i/xnr, 'HK'nts. \^. , L . . . . 



[Distance between the fascicles 0.20-0.30 mm. 



The tergopores are confused in every sense of the word; no section can cut 

 through their whole length, and they appear as an irregular network with large 

 meshes (fig. 16). They are polygonal exteriorly (figs. 12, 17). Their walls are 

 not thick (fig. 17) and the interstices left between them are filled with a compact 

 calcareous deposit, They are attached to the lamella and appear to be dorsal 

 ramifications of the zooecia. 



Affinities. The species differs from Pleitronea fibrosa and Pleuronea fenestrata 

 in the very special funnel-shaped form of the orifice of the tergopores. 



Occurrence. Midwayan (Clayton limestone) : Mabelville near Little Rock, 

 Arkansas (very common) ; 1 mile west of Fort Gaines, Georgia (common). 



C otypes. Cat. No. 65245, U.S.N.M. 



TRETONEA, new genus. 



Greek: treton^ opening, in allusion to the ovicells which are pierced by the 

 fascicles. 



The ovicell is lobate, subsymmetrical, median, elongated between the fascicles. 

 There are pores on both faces of the zoarium. The fascicles are arranged sym- 

 metrically on each side of the median axis. The oeciostome is placed at the be- 

 ginning of a fascicle. 



Genotype. Tretonea levis, new species. Lower Jacksonian. 



The nature of the pores is not known for the specimens were silicified and 

 it has not been possible to make sections. 



TRETONEA LEVIS, new species. 



Plate 141, figs. 20-27. 



Description. The zoarium is free, branched, with triangular sections; it bears 

 special pores on both sides. The fascicles are salient, quite close together, formed 

 of six to eight zooecia. The tubes are invisible and hidden under the pores; the 

 peristome is rectangular, thin and salient. The ovicell is smooth; the oeciostome 

 commences the second fascicle; it is a little larger than the apertures and turned 

 in the direction of the median axis. 



55899 20 Bull. 10619 



