PROBLEM OF THE MONTICULIPOROIDEA 1 65 



the whole forming a fenestrated frond with primary branches or 

 bars arising from an irregular basal attachment, and from these 

 a little narrower, parallel to slightly radiating ones. The fenes- 

 trules are rather wider than the bars ; ten bars occur in i cm . 

 They have celluliferous obverse side and solid reverse, the latter 

 on the outer or under side of the zoarium and forming the basal 

 expansion and sometimes rootlike anchors at intervals above it. 

 From the base a more or less funnel-shaped stalk supports the 

 large frond on one side. 



The cell apertures are about o.i3 mm in diameter and on the 

 bars are arranged in two rows, separated by a thin median ridge 

 which bears more or less prominent small warts or acantho- 

 pores. The dissepiments have distributed cell apertures only. 



The internal structure seen by thin sections consists of short 

 prostrate thin-walled axial cells arising mesially, turning sharply 

 into the peripheral region where they become surrounded by 

 interstitial solid deposit. Thus the cells have the appearance of 

 being thin walled "enclosed in a calcareous crust," since the 

 mesopore spaces on the obverse and the equally thick solid 

 deposit on the reverse, surround the cells. There is a median 

 wall or structure corresponding to the median ridge. The 

 reverse is longitudinally striated at first, later nearly smooth, and 

 its internal structure corresponds thereto. Further, it has been 

 claimed that the solid deposit on the obverse and reverse had 

 small vertical pores ending in minute warts at the surface, but 

 that the dim structures so interpreted were open tubes may well 

 be doubted. Another feature, the so-called dimorphic pores 

 (cells), arise in the solid deposit of the reverse and obverse, are 

 somewhat smaller than the regular cells but at the surface end 

 with slightly elevated peristome like these. They are not to be 

 wondered at, since they arise in what is homologous to mesopore 

 space in, for example Stellipora or Stictoporella, and may be taken 

 as evidence that peripheral cell increase had not wholly disap- 

 peared. The cells have no tabulae, but sometimes a hemi- 

 septum. 



The dissepiments in this zoarium are comparable both to 



