BRYOZOA. 419 



species is the unavoidable result, since but a small proportion 

 of the forty-two American species that had been previously re- 

 ferred to the genus are really congeneric with the typical form. 



TREMATOPORA DEBILIS Ulrich. 



PL XXXIV. flg. 3-3e. 



Zoarium consisting of slender, cylindrical, branching stems, 

 from 1.5 to 2 mm. in diameter. Surface smooth. Zooecial tubes 

 long, bending but little to reach the surface. Cell walls very 

 thin in the axial region, slightly thickened in the cortical region. 

 Zocecia with apertures circular or nearly so, about 0.15 mm. in 

 diameter, and surrounded by a peristome most elevated at the 

 lower end; closer together transversely than longitudinally, 

 there being about five in one direction and only four in the 

 other in 1 mm. Mesopores interspersed irregularly among the 

 cells, of unequal size, and closed at the surface. Acanthopores 

 few and inconspicuous. An occasional diaphragm is present in 

 in the zocecial tubes, and from one to three in the mesopores. 

 The cortical region, as shown by a transverse section, is very 

 narrow. 



From TV? nitida Or., this species is distinguished by its more 

 robust growth and larger and differently shaped cells. The 

 cortical region is thinner, and the curve of the zocecial tubes in 

 approaching the surface is greater in this species. From T. 

 primigenia Ulr., a Trenton species of Minnesota, it is easily dis- 

 tinguished by the lack of the maculae so characteristic of that 

 species. It differs too widely from the other described species of 

 the genus to necessitate comparison. 



Position and locality: (?) Cincinnati group, Alexander Co., 

 Illinois. 



TREMATOPORA? NITIDA Ulrich. 



PL XXXIV, fig. 2-2f. 



Zoarium consisting of small cylindrical stems, branching vari- 

 ously, 1 mm. or less in diameter. Zooecial tubes extending 

 obliquely outwards from the center of the stem, scarcely curving 



