EAKL.Y PALEOZOIC BEYOZOA OP THE BALTIC PROVINCES. 261 



quently these semidiaphragms are seen to be placed directly opposite 

 each other in the same tube. In such a case, the structure is exactly 

 the same as the centrally perforated diaphragm of Stenopora. At 

 other times the partition extends only partially around the circum- 

 ference of the cell and appears in sections as a single projecting semi- 

 diaphragm. 



The typical form of the species is illustrated in figure 152. The 

 regular hemispheric, solid zoarium is made up of a number of distinct 



Fig. 152.— Esthoniopoea communis, a, side view of an aveeage specimen, natueal size; 6, basal 



VIEW OF SAME SHOWING EPITHECA AND CICATRIX OF ATTACHMENT; C, TANGENTIAL SECTION, X20, OP 

 AVEEAGE ZOCECIA ; d, SEVEEAL ZOCECIA OF THE SAME SECTION, X35, ILLUSTEATING SIMPLE, AMALGAMATED 

 WALL STEUCTUEE; e, VEETICAL SECTION, X8, THEOUGH TWO ZOAEIAL LATEES; /, POETION OF THE SAME 

 SECTION, X20. JEWE LIMESTONE (Dl), BAEON TOLL'S ESTATE, ESTHONIA. 



zoarial layers, two of which are shown in the vertical section, figure 

 152 e. As usual in such zoaria, the tubes of these individual layers 

 are placed so nearly on top of each other that they form practically 

 one and the same tube throughout the colony. 



In figure 154 the zoarium consists of a single layer in which the 

 semidiaphragms are placed opposite each other with considerable 

 regularity. Whenever tabulae of this sort are cut by the tangential 



