THE EARLY PALEOZOIC BRYOZOA OF THE 

 BALTIC PROVmCES. 



By Ray S. Bassler. 



Curator of Paleontology, United States National Museum. 



INTRODUCTION. 



The Cambrian and Ordovician strata of Baltic Russia have been 

 the occasion of many paleontologic memoirs, mainly because the 

 rocks are composed in part of unconsolidated materials yielding an 

 abundance of most beautifully preserved fossils. The exquisite 

 preservation of these specimens, especially the trilobites, is attested 

 in museum collections the world over. The large number of species 

 in these strata is evident when it is known that in 1860, in his Lethsea 

 Rossica, Eichwald described or recorded the occurrence of no less 

 than 500 Ordovician forms and that since then many more species 

 have been added to the faunal list by other students. In this host 

 of species only a few American forms were recognized, indeed, almost 

 invariably no attempt has been made by either European or American 

 students to identify trans-Atlantic species. The splendid trilobite 

 fauna of the Russian Ordovician is undoubtedly the best known and 

 most completely described. Next in importance come the brachio- 

 pods and echinoderms, particularly the cystids, which have received 

 very detailed study. The moUusca, although numerous in described // 

 species, still require much investigation, but the ostracods and the 

 bryozoans are the least known of all the classes. 



In the present work I have endeavored to present as complete a 

 study of the Russian Ordovician Bryozoa as the available collections 

 would allow. It was my intention to limit the work to this subject, 

 but in the course of study several additions have been made. First, 

 the description of a single Cambrian form, of especial interest in being 

 the oldest known bryozoan, was added. Then, when the studies 

 were nearly completed, the authorities of the British Museum sent to 

 the United States National Museum for determination, two collec- 

 tions of Bryozoa obtained by Dr. F. A. Bather, from certain Ordo- 



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