BRYOZOA. 



317 



Fig. 6. a, vertical section of Ptllodictya variabilis TJL, x 35, showing several hemi- 

 septa; b, half of a slightly oblique vertical section of Ptilodictya maculata UL, showing 

 peculiar hollow spine-like processes projecting into the zocecial cavity. 



Upon careful examination it will be noticed that the supposed 

 diaphragms spring alternately from the two walls, and that 

 they do not extend to the opposite wall but terminate at some 

 point between them. 



The peculiar structures which I have called cystiphragms are 

 very characteristic of some of the most typical TREPOSTOMATA. 

 They are best shown by and almost restricted to the MONTI- 

 CULIPORID.E, comprising the genera Afonticulipora, Peronopora, 

 Prasopora, Homotrypa, Homotrypella and AtactoporeUa. 

 When examined in vertical sections of these genera, the cysti- 

 phragms are seen to form a series of lenticular vesicles on one 

 (rarely both) sides of the zocecial chamber. They are usually 

 joined to each other in such a way that they present the ap- 

 pearance of overlapping curved lines. In tangential sections the 

 vesicles are seen to extend around about two-thirds of the cir- 

 cumference of the cell chamber (or sometimes to encircle it) 

 their cut edges giving the appearance of an enclosed eccentric 

 tube within the zooecial cavity. The space between the inner 

 margin of the cystoid series and the opposite wall is inter- 

 sected by horizontal plates or ordinary diaphragms, which may 

 be as numerous as the cystiphragms. In species of Prasopora 

 (e. g. P. oculata and afiinis Foord, and P. selwyni Nich.,) the 

 cystoid diaphragms are often isolated so that they do not touch 

 each other at all. In this condition the structures compare very 



