EAELY PALEOZOIC BEYOZOA OP THE BALTIC PROVINCES. 307 



there are all degrees of gradation in the extent and elevation of the 

 maculae, so that little question can be raised as to the specific identity 

 of the forms here considered as synonyms. Comparing Dybowski's 

 figures, we find that in Trematopora cingulata (pi. 3, figs. 1, Ih) the 

 maculae do not rise above the general surface and are so elongated 

 transversely as to form encircling rings, T. cingulata var. nodosa 

 (pi. 3, fig. la) differs only in having these ring-like maculae shghtly 

 elevated. In T. variabilis (pi. 3, figs. 2, 2a) the maculae, although 

 transversely elongate, are arranged somewhat irregularly and the 

 acanthopores are more numerous. T. variabilis var. complanata (pi. 

 3, figs. 3, 3a) has the same zooscial structure and differs only in the 

 very irregularly shaped monticules. Dybowski's tangential sections 

 (pi. 3, figs, lb, 2a, 3a, 4a, and 4c) are sufficient in themselves to show 

 the identity of his various species, but the only illustration of T. 

 pustulifera (pi. 3, fig. 6) shows apparently a somewhat different 

 internal structure. Examination of Dybowski's type-specimen, 





'it%£: 



.5^^ 



Fig. 189.— Dittopoea colliculata. a, tangential section of a young example, X20, showing the 



CHAEACTEEISTIC SHAPE OF ZOCECIA AND THE LAEGEE SET OF ACANTHOPOBES; 6, VEETICAL SECTION OF 

 THE SAME SPECIMEN, X20. WASSALEM BEDS (D3), UXNOEM, ESTHONIA. 



kindly loaned by Doctor Mikhailowski, proves T. pustulifera to be 

 only a form of this same abundant Dittopora, with numerous well- 

 developed acanthopores and a zoarium without conspicuous maculae. 

 To show this identity, a figure of a tangential section prepared from 

 the type is introduced (fig. 190 b). Considering the numerous new 

 species of Trepostomata in the Russian Ordovician, it is odd that this 

 particular form should have received so many names. The following 

 description is believed to cover the essential characters of the species. 

 Zoarium growing from a rounded or somewhat pointed base into 

 straight, cylindrical, rather infrequently dividing branches, var3dng 

 from 3 mm. to 10 mm. or more in diameter. Surface with more or 

 less elongated solid maculae composed of closed mesopores bordered 

 by a row of zocecia slightly larger than the rest. Maculae often 

 transversely elongated to such an extent that frequently several 

 coalesce and form a continuous uncelluliferous band about the branch. 



