322 PALEONTOLOGY OF ILLINOIS. 



ing levels in contiguous tubes. This brings us to a point which 

 ought never to be lost sight of in the study of Palaeozoic Bry- 

 ozoa. Namely, that in the TKEPOSTOMATA and many CRYPTO- 

 STOMATA, the tubular zooecium really represents a series of super- 

 imposed cells. This fact is very well shown in fig. Ga represent- 

 ing a vertical section of P. vari&bilis. Upon examination, it 

 is clear that each tube in this section contained two successive 

 zocecial chambers, each of which was provided with its own 

 superior and inferior hemiseptum. In P.pavonia and P. maculata 

 the last structures are repeated at much shorter intervals, but 

 on account of their extreme delicacy are rarely preserved. Re- 

 turning to the consideration of the spine-like projections, I find 

 that they resemble the radiating spines which occur in the 

 tubes of several species of Heteropora and Ceriocava ramulosa, 

 D'Orb. In these also the spines are developed at correspond- 

 ing levels in contiguous tubes. Next I would suggest a com- 

 parison with the spines which project from the walls and over 

 the cells in a number of recent species of Membranipora (e. g. 

 M. spinifera Johnston, M. lineata Linn. (Hincks.) 



