2 2 FREDERICK W. SARDESON 



Tabulae perhaps need no special mention ; their character 

 as the successive bottoms of the calycals is entirely evident 

 (Plate A, Fig. 2, and Fig. I, h, p. 21). In structure, if any 

 be seen, they are one-sided. E. O. Ulrich has observed the 

 very rare occurrence of perforation or circular opening in the 

 last tabula, which he interprets to prove that all other tabulae 

 are double, comprising the amalgamated cover of one zocecium 

 and bottom of a next superimposed zocecium. In absence of 

 any substantiating evidence it is better to take the most direct 

 explanation, which would be that the observed perforated tabulae 

 were left incomplete by the death of the colony. Indeed, in 

 Hemiphragma, the tabulae of the cells in the peripheral region 

 are all left incomplete or were imperfect as to calcareous struc- 

 ture. The surfaces of tabulae are sometimes papillated, and these 

 again, like the acanthopores, simulate perforations in the fossil- 

 ized specimen. 



As a rule, neighboring cells do not have corresponding 

 tabulae, either in position or number. In any species or individ- 

 ual they are approximately regular in position and numbers, 

 but never quite so. In different species the number ranges in 

 extremes from none, as seen in the axial region of some species, 

 to very many in others, or even to a compacted papillose mass 

 filling the cells, or especially the mesopores in some thick-walled 

 forms. There is no unit form and size of loculus assignable, 

 which argues very strongly against any theory that the succes- 

 sive loculi represent superimposed zocecia. The clearer inter- 

 pretation is that each cell was built by one zooid. Tabulae are, 

 as a rule, very thin ; and tabulae wanting and tabulae thickened 

 are opposite degrees. Individual variation and specific differ- 

 ence in number and thickness of tabulae may be ascribed to 

 difference of growth and to secretion of substance. Difference 

 in form, such as the cystiphrams (Prasopora) , are ascribable to 

 shape and size of the zooids' base ; and vesiculose mesopores, to 

 shallow or closed calycals from short zooids, and to their shift- 

 ing, possibly, also. 



