ART. 21 CYCLOSTOMATOUS BRYOZOA CANU AND BASSLER 53 



Genotype. — Pleihopora verrucosa Hagenow, 1851. Cretaceous 

 (Aptian, Maastrichtian), 



The place of the nematopores is variable in the Cytisidae, according 

 to the nature of the genera. In Pletliopora they are arranged entirely 

 around the zoarium, while m other genera they are found only on the 

 dorsal. 



PLETHOPORA APTENSIS. new speciea 



Plate 7, figs. 3, 4 



Description. — The zoarium is free, cylindrical, bifurcated. The 

 zooecia are grouped in fascicles, which are salient and orbicular. 

 The nematopores are small, polygonal, arranged entirely around the 

 zoarium. 



Measurements. — Diameter of fascicles, 0.56 mm.; diameter of 

 branches, 2 mm. 



Structure. — In longitudinal section the tubes are cylindrical, long, 

 with peripheral gemmation; they occupy the essential and principal 

 part of the zoarium. The nematopores appear solely on the zoarial 

 margin in small spaces between the fascicles, thus confirming the 

 thin section of Hennig. 



In transverse sections the larger tubes are in the middle. These, in 

 branching, engender the axial tubes of the fascicles. On the borders 

 the small pores are those of the peripheral nematopores. 



Affinities. — The distinction between the species of this genus is 

 rather difficult to make from the published figures. Comparisons of 

 specimens, on the contrary, permit a differentiation, according to the 

 relative size of the orifices, of the nematopores, and the form of the 

 fascicles. The circular form of the latter and the large size of the 

 zoarium well characterize this species. 



Occurrence. — Lower Cretaceous (Aptian) : Faringdon, England 

 (rare) . 



Cotypes.— Cat. No. G9903, U.S.N.M. 



Genus PLETHOPORELLA Canu and Bassler, 1922 



The ovicell is elliptical, elongated, large, little convex, smooth. 

 The tubes are cylindrical, without peristome, with orbicular orifice; 

 their walls are moniliform; they are recurved at their extremity. 

 The gemmation is peripheral around a bundle of axial tubes. No 

 adventitous tubes. 



Genotype. — PletJioporella (PletTiopora) ramulosa D'Orbigny, 1847. 



Range. — Cretaceous (Campanian, Maastrichtian). 



History. — D'Orbigny was in error in comparing the genotype with 

 Pletliopora verrucosa Hagenow, 1851. The internal structure is very 

 different, for not only are there no nematopores but the tuberosities 

 which ornament the zoarial surface are not formed of bundles of 

 tubes. 



