NORTH AMERICAN EARLY TERTIARY BRYOZOA. 355 



The fossil species are : 



Schizomavella (Schizoporella) lata MacGillivray, 1895. 



Schizomavella (Schizoporella) plagiostoma MacGillivray, 1895. 



Levinsen in 1909, thought that median avicularia characterized the Smittinidae 

 and that they might not exist in the Escharellidae. The Schizoporellae provided 

 with a median avicularium might be reunited with the Smittinidae under the name 

 of Smittina. The work of Harmer in 1902 J showed that in Schizoporella lineai'is. 

 the compensatrix and the hydrostatic system are analogous to those of the other 

 Schizoporella and are notably different from those of Smittina trispinosa. Under 

 these conditions we think we must maintain the primitive nomenclature. To 

 facilitate the determination we have created the genus Schizomavella for the species 

 provided with a very constant median avicularium. 



The distinction between Schizomavella and certain species of Hippoporina is 

 easy to make on the recent specimens by an examination of the muscular attach- 

 ments on the operculum. On the fossil forms, the interior may furnish some 

 useful points, but very often the problem is insoluble, so we must content our- 

 selves with simple comparisons. 



SCHIZOMAVELLA GRANULIFERA, new species. 



Plate 46, figs. 4-12. 



Description. The zoarium is free, with flat or undulated fronds formed of 

 two lamellae, back to back, and inseparable. The zooecia are distinct, elongated, 

 fusiform, separated by a furrow or a prominent thread; the frontal is convex, 

 ornamented with small tremopores and small granulations. The aperture is trans- 

 verse, elliptical ; the rimule is very wide and separated from the anter by two 

 small cardelles. The aperture of the ovicelled zooecia is larger. The ovicell is 

 globular, very salient, ornamented by the same tremocyst as the frontal; it is 

 hyperstomial, but always closed by the operculum. The median avicularium is 

 small, round or triangular, adjacent to the rimule. 



f#a=0.10-0.12mm. . fZs=0.54-0.70mm 



Measurements. Aperture \ 7 Zooecia , 



U=0.r2-0.14mm. U2=0.34-0.50mm. 



Variations. This species is very variable and its study has given us much 

 trouble. The numerous specimens collected at many localities permit the recog- 

 nition of the principal variations. The micrometric dimensions vary in unusual 

 proportions; the zooecial length varies from 0.50 mm. to 0.80 mm. and the width 

 from 0.30 to 0.52 mm. It is the same with the aperture, the dimensions of which. 

 rather fixed on a single specimen, vary a great deal, according to localities. The 

 frontal granulations are attenuated (fig. 10) or very salient (figs. 5, 8). The 

 zooecial margins are sometimes very salient (fig. 10), but they are wanting most 

 of the time (figs. G, 8). The avicularium is generally round, but it may be much 

 removed from the aperture and become triangular (fig. 9). The ovicell covers 



1 1902. Harmer, ou the Morphology of the Cheilostomata, Quarterly Journal Microscopical Science, new 

 ser., vol. 46, p. 301, pi. 17, figs. 42, 46, 4S. 



