52 



PEOCEEDINGS OF THE NATIONAL. MUSEUM 



The base of the small zoarium is pointed, but in the large zoaria 

 it is somewhat wider; they are flabelliform, and it is difficult to 

 understand how they were able to maintain equilibrium on their 

 support. 



In longitudinal section the tubes are long, cylindrical, with intra- 

 zoarial gemmation; the walls are vesicular but with very small 

 elements. The zoarial walls are thickened. 



Occurrence. — Lower Cretaceous (Valangian) : Sainte-Croix (Vaud), 

 Switzerland. 



Plesioty pe.—Csit. No. 69902, U.S.N.M. 



Family CYTISIDAE D'Orbigny, 1854 



Genus CYRTOPORA Hagenow, 1851 



CYRTOPORA CAMPICHEANA D'Orbigny, 1853 



1853. Cyrtopora campicheana D'Orbigny, Paleontologie frangaise, Terrain Cre- 

 tac6, vol. 5, p. 673, pi. 761, figs. 14, 15. 



Fig. 25. — Genus Plethopora Hagenow, 1851. A, B. Plethopora malmi Hennig, 1894. A. Zoarium, X 2.6. 

 B. Longitudinal section magnified, showing zooecial tubes (z) and the nematopores (/) (A, B, after Hen- 

 nig, 1894). Upper Cretaceous of Sweden. C,!). Plethopora aptensis, new species. C. Longitudinal sec- 

 tion, X 16, showing the nematopores with thickened walls and the large axial tubes. D. Transverse 

 section, X 16, exhibiting the base of the saliant fascicles with open tubes and the thin zone of nemato- 

 pores. Lower Cretaceous (Aptian): Faringdon, England 



Our transverse section confirms that of Gregory, 1909. The tubes 

 are very large, polygonal, with thin adjacent walls. 



Occurrence. — Lower Cretaceous (Valangian): Sainte-Croix (Vaud), 

 Switzerland. 



Plesiotype.— Cat. No. 69950, U.S.N.M. 



Genus PLETHOPORA Hagenow, 1851 



1851. Plethopora Hagenow, Die Bryozoen der Maastrichter Kreidebildung, 

 p. 45. 



The tubes are cylindrical; they are grouped in salient, orbicular 

 bundles opening in all directions. The nematopores are arranged 

 entirely around the zoarium. 



