16 BULLETIN" 77, UNITED STATES NATIONAL MUSEUM. 



species. The large number of species determined from the Wassalem 

 beds was made possible by the study of the Mickwitz collection 

 which was especially rich in bryozoans from this division. 



E. Wesenberg limestone. — Succeeding the Jewe limestone is an 

 equally fossiliferous and widespread formation of thin limestone and 

 shale named from its occurrence at Wesenberg. Both the limestones 

 and shales of the Wesenberg are of a yellowish color and seldom 

 exceed 30 feet in thickness. 



The fauna of the Wesenberg limestone is strikingly like that of the 

 lowest Trenton strata of the United States, classed under the names 

 Clitambonites, Nematopora, and Fusispira beds. Several species of 

 Clitamhonites occur in the Wesenberg, and in America the earliest 

 occurrence of the genus is in the bed named for it. At least one of 

 the species in the two areas is not very dissimilar. Other species of 

 brachiopods which are common to the two beds, or are represented 

 by closely related forms, are Dalmanella testudinaria (small variety), 

 PlectortJhis plicatella, Plectambonites sericeus (variety), StropJiomena cfr. 

 scqfieldi, and Rafinesquina cfr. deltoidea. 



The Russian Wesenberg pelecypods have not been studied in detail, 

 but specimens before me, in a few cases, resemble American forms. 

 The gastropods of both areas are well known and show some similarity; 

 thus the large Pleurotomaria insignis Eichwald is certainly the same 

 as HorTnotoma major Hall, from the earliest Trenton of Missouri and 

 Minnesota, and the Russian examples of Maclurea neretoides Goldfuss 

 are close to American species. Among the corals a Protarea and a 

 Streptelasma like S. profundum, are represented in each area. Con- 

 siderable resemblance is shown in the bryozoans, indeed, a slab of the 

 Wesenberg limestone covered with numerous examples of Hallopora 

 goodliuensis, Eridotrypa sedilis and variety minor, Pachydictya elegans, 

 and with the incrusting Corynotrypa inflata, resembles very greatly 

 material from the Clitambonites bed. 



F. LyckTiolm and Borldiolm. — The uppermost strata of the Baltic 

 region assigned to the Ordovician by authors, comprise gray to white 

 limestones attaining a thickness of 65 feet and restricted to Esthonia 

 and the islands of Worms and Dago. Schmidt recognized two zones 

 in this formation, which he designated F, a lower Lyckholm zone 

 (Fl), of gray and yellow, sometimes dolomitic limestone, and an 

 upper Borkholm zone (F2), of hard, white siliceous limestone. The 

 faunas of the Borkholm and of the upper part of the Lyckholm are 

 essentially the same and upon their evidence no necessity exists for 

 recognizing two zones. The bryozoans, ostracods, and corals of 

 these beds are of genera and often of species characteristic of the 

 Richmond formation of America. Among the corals, for example, are 

 species of Tetradium, Favosites, Heliolites, Plasmopora, and Calapcecia, 

 an assemblage of forms that, on the whole, is distinctly Silurian in 



