EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 259 

 ESTHONIOPORA, new genus. 



The value of the minute wall structure as a reliable character in 

 classification is well exemplified in the group of species for which this 

 new name is proposed. At first the two species now assigned to 

 Esthoniopora were regarded as somewhat aberrant forms of H&mi- 

 pliragma, but more detailed investigation of the walls showed that 

 those of adjacent zooecia were fused together as in the Amalgamata 

 and were not separated by the distinct dark line characteristic of the 

 Integrata. Further study has convinced me that Esthoniopora is a 

 member of the Batostomellidse and not far removed from the late 

 Paleozoic genus Stenopora. Indeed, it is possible that the genus is the 

 simplest expression of the stenoporoid type of structure. The arrange- 

 ment of the diaphragms in E. communis is highly suggestive of 

 Stenopora, although the beaded walls and the acanthopores of the 

 latter genus are wanting. 



Esthoniopora may be defined as follows: 



Zoarium massive, hemispheric, with a flat, concentrically wrinkled 

 base; composed of thin-walled, polygonal zocecia in close contact; 

 walls of great simplicity but clearly amalgamated; acanthopores and 

 mesopores absent; zocEcial tubes with semidiaphragms which, in the 

 type species, are frequently placed opposite each other, and in a second 

 species, are large and curved enough to resemble a cystiphragm. 



Genotype. — Esthoniopora communis, new species. Middle Ordo- 

 vician of Russia and Sweden. 



The diagnostic features of Esthoniopora are the massive zoarium, 

 polygonal zooecia with amalgamated walls and semidiaphragms, and 

 the absence of acanthopores and mesopores. All other genera of the 

 Batostomellidse except Stenopora differ so obviously that comparisons 

 are hardly necessary. The relations between Stenopora and Esthonio- 

 pora have been discussed above. The most difficulty will be experi- 

 enced in separating the species of this new genus from the simple 

 massive types of Hemiphragma, and thin sections are necessary to 

 show their distinct wall structure. 



In this connection it may be mentioned that both of the species of 

 Esthoniopora agree in having their zooecial tubes filled with coarsely 

 crystalline calcite, which reflects and refracts the light so much that 

 vertical fractures often present an iridescent effect. This character, 

 if it may be so called, is not limited to the present genus, for all of 

 the species of Calloporina and Anaphragma show the same structure, 

 while other genera show no trace of it. I am thus led to believe that, 

 although this is a purely physical character, it has an organic basis and 

 is thus of value in the discrimination of certain genera and species. 



According to present knowledge, species of Esthoniopora are un- 

 known in American strata, and in Europe are confined to the Middle 

 Ordovician rocks of Esthonia and the neighboring Baltic Provinces. 



