PROBLEM OF THE MONTICULIPOROIDEA 7 



approximately equal, and, like the cell throughout, are polyg- 

 onal or hexagonal by reason of contact (PI. A, Fig. i). The 

 incipient or expanding parts of cells are seen there as small tri-, 

 or quadrangular openings at the angles between the older, larger 

 cells. Crowding of the cells appears to prevent entire regularity 

 in shape and size of each cell, and the walls are crenulate. 



In speaking of cell one includes for each the half of the 

 bounding wall, although the walls originally are dense, amalga- 

 mated, calcareous structures, not double further than that they 

 were built not only by increment upon their margins, but also 

 on the two surfaces. Theoretically there is a boundary plane or 

 division between cells midway in the wall. They frequently 

 split midway in the wall when fractured. The walls in this 

 species are thin and show little or none of their growth struc- 

 ture. At a slight depth within each cell the last growth incre- 

 ment or layer crosses the cell opening and forms a transverse 

 partition or false bottom, the so-called tabula. Tabulae occur 

 successively in all cells more or less regularly, but not corres- 

 ponding in neighboring cells. They are a little more numerous 

 in the incipient part of each cell. The wall edge of one cell 

 cannot extend above those of its neighbors, from which it never 

 separates. 



The zoarium corresponds in structure to the following sup- 

 posed manner of growth : It was covered when alive by numer- 

 ous equal sized zooids which coalesced laterally, the lower part 

 of each, however, extending into and secreting the walls forming 

 the cell or zocecium. Young zooids arose among them and, 

 growing, extended relatively downward, building a new cell ; the 

 increase in number of zooids and, respectively, cells, being com- 

 pensated by a necessary growth in radial length of cell wall to 

 increase the surface of the inhabited zoarium. The tabulae indi- 

 cate successive planes where the bottom of the zooid rested 

 between periods of necessitated self-extraction from the ever 

 too long cell. 



E. O. Ulrich assumes that the cells are " Zocecia, directly 

 superimposed upon one another so as to form long tubes 



