EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 17 



character, A similar coral zone is widespread in the Richmond 

 group of western North America, where it follows argillaceous and 

 magnesian rocks of Galena-Trenton age. 



. Although there is no direct evidence in pubhshed work, it seems 

 probable that a similar Galena-Trenton zone underhes the coral beds 

 of the Lyckholm. In a fauna collected from the lower Lyckholm by- 

 Prof. Schuchert, every species is closely related to forms from the 

 typical Galena of the Mississippi Valley, and elsewhere in North 

 America. At many places to the north, west, and east of Minnesota 

 the Galena fauna is followed directly by the coral bed of the Rich- 

 mond. In America the hthology of these Galena-Trenton and 

 Richmond strata is so similar that both have been uniformly included 

 in a single magnesian hmestone formation. Without the evidence 

 of the fossils the presence of a great time break in this formation 

 might not be suspected. The bryozoans of the lower Lyckholm 

 are, hke those of the American Galena, distinctly Trenton in character, 

 while those of the upper Lyckholm and Borkholm include char- 

 acteristic American Richmond species. 



These latter strata also contain small forms of an undoubted 

 Atrypa, Leptsena rhomhoidalis, a typical Streptis, a Striclclandinia, 

 and other brachiopods of Silurian affinities. Of the 19 species of 

 Bryozoa identified in the Lyckholm, 5 can not be considered in 

 correlation, as they are here described for the first time. Five 

 additional species of the list either are known to come from the 

 lower beds of the formation or are long ranged geologically. Of 

 the remaining 9, Corynotrypa ahrupta Bassler, Nematopora fragilis 

 LTlrich, and AnapJiragma mirahile Ulrich and Bassler are charac- 

 teristic Richmond fossils, while Corynotrypa dissimilis (Vine), 

 Pachydictya lifurcata (Hall), Glauconome plumula Wiman, Orhigny- 

 ella expansa haltica, new variety, and Hallopora elegantula (Hall) 

 are either identical or closely related to typical Silurian brj^ozoans. 

 Thus on the evidence of the bryozoans the upper Lyckholm is of 

 early Silurian age. 



The bryozoan fauna of the Borkholm is clearly of Silurian age, 

 since practically every species is of a well-known Richmond or early 

 Niagaran type. The list of the strictly Borkholm species, with 

 their occurrence in America or their American representative added 

 in parentheses, follows : 



List of Borkholm Bryozoa. 



Corynotrypa dissimilis (Vine) (Niagaran of America.) 

 Ptilodictya fiahellata Eichwald (Ptilodictya expansa Hall). 

 Ptilodictya gladiola Billings (Richmond of America). 

 Pachydictya bifurcata (Hall) (Niagaran of America). 

 Sceptroporaf acuta Ulrich (Richmond of America). 



