18 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Nematopora lineata (Billings) (Richmond of America). 



Glauconome plumula Wiman (Glauconome sp., Niagaran of America.) 



Glauconome strigosa (Billings) (Richmond of America). 



Lichenalia concentrica Hall (Niagaran of America). 



Hallopora elegantula (Hall) (Niagaran of America). 



Chasmatopora tenella (Eichwald) (Chasmatopora angulata Hall, in early Niagaran 



of America). 

 Fenestellastriolata^icloLwald (Fenestella granulosa WhitAeld, Richmond of America). 

 Protocrisina exigua Ulrich (Richmond of America). 

 Phsenopora ensiformis (Hall) (Early Niagaran of America). 

 Pseudohornera orosa (Wiman). 



In the following table I have given the figures showing the total 

 number of bryozoan species in the various Kussian formations in 

 the first column and the number of American species common to 

 the two areas in the second. With scarcely an exception, all of 

 these American Middle Ordovician species are from the Black Kiver 

 group and the earliest Trenton, while the American speciecs, found 

 also in the upper Lyckholm and Borkholm, are all of early Silurian 

 types. 



Summary of Baltic and American Ordovician and Early Silurian Bryozoa. 



Formation. 



Early Silurian. 



Borkholm limestone (F2) 



Lyckholm limestone (Fl) (including the lower part, of possible Middle Ordovi- 

 cian age) 



Middle Ordovician. 



Wesenberg limestone (E) 



Wassalem beds (D3) 



Kegel beds (D2) 



Jewe limestone (Dl) 



Itferbeds(C3) 



Kuckers shale (C2) 



Echinospherites limestone (01) 



Orthoceras limestone (B3) 



Glauconite limestone (B2) 



Total num- 

 ber of Bal- 

 tic species. 



Number 

 of species 

 common to 

 American 

 and Baltic 

 areas. 



Summarizing the foregoing remarks, it would appear, from a 

 study of the Bryozoa, at least, that the Russian Baltic section is 

 far from complete; indeed, is composed of fragments only of the 

 great North American sequence. Thus the entire Cambrian is repre- 

 sented by only a few hundred feet of strata, and all of the Canadian 

 by the thin Dictyonema beds, probably of Beekmantown age. 

 Beginning with the invading Glauconite sandstone and continuing 

 until the close of the Wesenberg, the faunas are uniformly of Middle 

 Ordovician age and represent the Black River and earhest Trenton 

 formations of the American section. A later Trenton horizon is 

 probably represented in the lower Lyckholm. The remainder of 



