1 68 FREDERICK W. SARDESON 



margins, and solid obverse of reticulate ones are mesopore areas 

 being seen sometimes as such [e.g., Stictoporella, Phylloporina pars, 

 Semicosmium) , and are probably all really maculse covered by 

 subordinated zooids, or at least a cortex. Longitudinal median 

 ridges and walls arise variously. Again, in jointed forms 

 {Ptilodictya, Arthropora, et al.) part of the skeleton was not cal- 

 careous. These show reduction from the entirely calcified 

 zoarium, and also the filling up of mesopores and some autocells 

 might be readily interpreted as due to leveling down of division 

 walls between zooids : a process of reducing thin-walled cell mass 

 to a solid axis within a living cortex. 



A quite different interpretation from that just given is 

 expressed in the current definitions of Cryptostomata. Vine 1 

 defined them, " Zocecia tubular, subtubular, in section slightly 

 angular. Orifice of cell surrounded by vestibule, concealed." 

 He does not speak of tabulae, mesopores, acanthopores, etc., and 

 only later knowledge, especially by E. O. Ulrich, has changed 

 the definition, adding to vestibule, "which may be intersected by 

 straight diaphrams or hemisepta owing to superimposition of 

 layers of polypides," "surrounded by vesicular tissue or solid 

 calcareous deposit." Vine, having in mind such as Septopora and 

 Ptilodictya without tabulae, seems to consider the cell as a per- 

 manently occupied zocecium ; Ulrich includes the richly tabu- 

 lated Pachydictya, Phylloporina, etc., and speaks therefore of 

 superimposition of polypides or zocecia. More direct inter- 

 pretation would indicate each cell to have been gradually 

 built and evacuated by one zooid, as argued in the preceding 

 pages. For corresponding explanation of hemisepta see text, 

 p. 161. 



The separation of Cryptostomata from Trepostomata is 

 scarcely tenable, and they may be discussed together. The 

 zoarium of Cryptostomata is merely the more differentiated, the 

 simplest Trepostomata and the typical Cryptostomata being 

 extremes in the same line. This developmental series might 

 well be compared to the reduction of thin-celled Tabulate corals 



'Brit. Assn. Rep., 1883, p. 184. 



