301 



Fig. I. Leioclema foliatum, UL Warsaw beds, Warsaw, DL a, Vertical section x28. 

 showing entire thickness of zoarium, tabulation of zocecia and mesopores, and struc- 

 ture of the aeanthopores : b, tangential section x28, showing distribution of acanthopores, 

 mesopores and zooecia; c, small portion of wall x50: d, acanthopore x50, showing its 

 structure. 



Further examination shows that they are composed of lami- 

 nated sclerenchyma, disposed in a concentric manner around a 

 circular clear or dark central space. In vertical sections the 

 minute central canal is often clearly seen, as well as the struc- 

 ture of the thick walls. The concentrically laminated structure 

 noticed in tangential sections proves to be produced by a succes- 

 sion of overlapping conical layers of sclerenchyma. This arrange- 

 ment of the laminae proves conclusively that the aperture of the 

 spines was at all times approximately of the same diameter, 

 and completely overthrows the supposition advanced by Dr. 

 Nicholson (''The Genus Monticulipora", p. 47), that these 

 spines were a peculiar form of corallites, the mouths of which 

 became closed by secondary deposit as the corallum assumed its 

 final characters. On the same page he also says: ''It is not, of 

 course, essential that we should suppose these singular struc- 

 tures to be occupied by polyps; but I think them to be modified 

 zooids in the same sense as is true of the 'avicularia' of the 

 Polyzoa''. I am perfectly willing to accept Dr. Nicholson's 

 view as it is expressed in the above quotation, since I am fully 

 convinced that in the "acanthopores" we are dealing with 

 structures that supported appendages most likely of identical 

 nature and functions with the avicularia or vibracula found on 

 recent Bryozoa. This explanation possibly applies only to the 

 large acanthopores as they are seen in Dekayia,, species of 

 Leioclema. and other forms. The smaller and closely arranged 



