PROBLEM OF THE MONTICULIPOROIDEA I 3 



expand quickly, and are scarcely tabulated and very unlike 

 mesopores of the peripheral region, and they are not called 

 mesopores. The mesopores of the axial region are not imma- 

 ture cells but permanently retarded ones. 



With this species is conveniently compared B \Hemipliragma) 

 ottawaense Foord, in which the thin-walled axial and thick-walled 

 peripheral regions are sharply defined, as seen in thin section or 

 in fractured specimens. At the stage when peripheral region is 

 just begun one sees characters very like B. fertile, but later the 

 walls thicken more, the mesopores are obscured, closed, or filled, 

 while the maculose-looking monticules show strongly diverging 

 cells, indicating slow growth in cell length compared to width. 

 Acanthopores developed. The tabulae are peculiar, being often 

 thickened and incomplete, hemiphragms, in the peripheral 

 region. The whole wall in the fossil is corneus looking. They 

 show the result of a decrease probably of calcareous constituent. 



Eridotrypa mutabilisUh. includes rather small, long, branched, 

 acrogene zoarial parts in which, as seen in cross fracture or sec- 

 tion, the cells are larger in the axial region than in the periph- 

 eral. The cells turn very slowly in the peripheral region, so 

 that the apertures are oblique to the surface and drawn out 

 anteriorly. Then, as the cells become more direct, the walls 

 increase steadily in thickness, and in very " old " specimens 

 distinctly cup-shaped calycals form (PI. A, Fig. n). The 

 thickened wall permits analysis into the bounding edge with its 

 projection downwards, as dividing lamina, and the calycal slope 

 and the main wall below it (r/. Fig. i, k, p. 21). 



Anolotichia impolita Ulr. has irregular large acrogene zoaria, 

 with large cells of quadrangular rather than polygonal outline, 

 and with few mesopores, reminding of Monotrypa magna (PI. A, 

 Fig. 12). The axial and peripheral regions are scarcely distin- 

 guished. In the latter stage there are, however, lunaria developed. 

 The lunarium occurs in the posterior side of a full-sized cell as a 

 narrow, distended part of the cell. The term lunarium has been 

 applied rather to the lunarial wall, which is narrowly arcuate or 

 crescentic. Where the lunarial and common cell walls join, in 



