EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 213 



mesopores are often practically indistinguishable. The acanthopores 

 are small but occur in such numbers in the mature zone that they give 

 a minutely spinous or granular aspect to the zoarial surface. 



Thin sections show this to be a typical species of Stigmatella. Ver- 

 tical sections exhibit thin, sUghtly crenulated tubes in the immature 



Fig. 116.— Stigmatella inplecta. a, side view of the type-specimen, natueal size; 6, tangential 



SECTION, X20, WITH ONLY A SMALL POKTION CUTTING THE KEGION OF ACANTHOPORES; C, ANOTHER TAN- 

 GENTIAL SECTION, X20, PASSING THROUGH A WELL-DEVELOPED ZONE OF ACANTHOPORES; d, SEVERAL 

 ZOCECIA OF THE SAME SECTION, X40, WITH THE STRUCTURE OF THE WALLS AND ACANTHOPORES CLEARLY 

 shown; C, VERTICAL SECTION, X20, SHOWING BOTH IMMATURE AND MATURE REGIONS. ORTHOCEEAS 

 LIMESTONE (B3), PORT KUNDA, ESTHONXA. 



region. These thicken somewhat in the mature zone with the devel- 

 opment of numerous acanthopores. The latter region is further dis- 

 tinguished by having an occasional diaphragm in the mesopores. 

 Tangential sections vary in appearance according to the zone which is 

 cut. In figure 116 &, the section passes through portions of both the 



