156 FREDERICK W. SARDESON 



a branch widened and narrowed repeatedly, but they usually 

 grew uniformly for a great length. Branches are twisted, helio- 

 tropic. 



This highly developed zoarium has equally modified cells. 

 As in Pacliydictya there is a mesial lamina or wall and the thin- 

 walled, prostrate, short, axial parts of cells are in single series on 

 either side, without mesopores, rectangular, or in part drawn out 

 obliquely toward the zoarial margin. The peripheral cell part 

 is sharply defined, both by obliquely outward direction and by a 

 thick complex wall between autocell openings, which are thus a 

 diameter or more apart. This wall comprises the cell walls 

 which appear thin, and between them a mesopore space. In 

 transverse and longitudinal thin sections one may see a tabulated 

 mesopore followed by filled mesopore space, to which the cell 

 walls are amalgamated on either side. What is most novel is a 

 strong dark line or wall dividing the mesopore space. On the 

 surface the mesopore space is elevated, rarely depressed, and the 

 cell aperture rows are in furrows, separated by strong continuous 

 longitudinal papillose ridges, and the apertures in each row by 

 lower short transverse ones. The ridge may be double or again 

 discontinuous, exceptionally. The ridges are the structural 

 cause of the dark line or wall seen within the filled mesopore 

 space. Maculae have closer parallel ridges, and the zoarial 

 solid margins may appear puncto-striate. 



This structural development appears due to the chaining 

 of zooids longitudinally, probably by a canal system which 

 impressed the longitudinal furrows or troughs, causing the 

 mesopore space to be relatively raised. These furrows end at 

 the growing apices of the zoarium, where cells, respectively 

 zooids, were increasing rapidly. As the growing apices became 

 more remote from a given part or ceased, the furrows filled 

 gradually, and a more allsided relation arose between the 

 cells. 



No mesopore calycals have been detected and the mesopore 

 space being confluent with the cell calycals, and so far subordi- 

 nated and fused to the autocell walls, one might conclude that 



