BRYOZOA. 321 



so many of the FAVOSITID.E has yet been detected in any bryo- 

 zoan. In a number of forms, however, there are indentations 

 of the wall which a superficial observer might mistake for such 

 structures. In most cases these inflections are produced by the 

 developement of "acanthopores" in the walls of the zooecia. 

 They are well shown in Atactopora, Atactoporella, Amplexopora 

 septosa, Batostoma implication Nich., and Heterotrypa inflecta. 

 In a few other cases of which Actiuotrypa peculiaris Rominger 

 (PI. LXXVII, fig. 3, 3a, 3b) and Glyptopora keyserlingi Prout, 

 may be mentioned, there are vertical ridges on the inner side 

 of the walls, which are not produced by acanthopores. In A. 

 peculiaris these ridges terminate at the surface as spine-like 

 projections on the peristome of the cell. Their number, though 

 varying from six to ten, is usually eight or nine. When exam- 

 ined in tangential sections they are found to be best developed 

 near the surface, and that, as the section cuts the zoarium at 

 a deeper level, they gradually become more and more obtuse 

 till they are no longer recognizable, the cell aperture having at 

 the same time been traced to its primitive circular form. In 

 Glyptopora keyserlingi the inflections are both less numerous 

 and less defined, as well as much more irregular. Ordinarily 

 two of them occupy positions in the wall opposite to the 

 lunarium. 



In the species of Ptilodictya (especially the section of the 

 genus typified by P. pavonia D'Orb., and P. maculata) I have 

 often observed certain tooth-like processes which project, from 

 the walls into the interior of the visceral chamber. In large ex- 

 amples of P. maculata and P. MH, they are often very numer- 

 ous, several tangential sections of the first species now before 

 me exhibiting from two to four in each cell. I have also re- 

 cognized them in vertical sections of this species, (see fig. 

 6b) but here they sometimes look so much like perforations in 

 the wall that I originally described them as such.* Perhaps it 

 is not now possible to give a satisfactory explanation of these 

 singular projections, still a comparison with several recent Bry- 

 ozoa may give us a clue to their nature. In the first place we 

 find that the spine-like projections are developed at correspond- 



* Am. Pal. Bry. Jour. Gin. Soc. Nat. Hist. voL V, p. 163, 1882. 



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