EARLY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 305 



Occurrence. — A common fossil in the Glauconite limestone (B2) 

 at Popowka, Tswos, Wassilkowa, Oberchow, Grenaj a Sheldacha, and 

 other localities in the government of St. Petersburg. Less abundant 

 in the Orthoceras limestone (B3) on the island of Rogo, near Bal- 







Fig. 187.— Dittopora annulata. a, tangential section of a mature example , X 20, passing through 



THE OUTER DEPOSIT OF INTERZOCECIAL TISSUE IN WHICH THE MESOPORES ARE BARELY \^SIBLE; 6, AN- 

 OTHER tangential SECTION, X20, CUTTING A MACULA AT A LOWER LEVEL AND EXHIBITING THE MESO- 

 pores; c, vertical section, x20, of a young example, showing the occurrence of semidia- 

 phragms nsr the bend from the immature to the mature region; d, similar section of aii older 

 specimen, x20, with the mesopores well developed and their outer portions filled by tissue. 

 Glauconite limestone (B2), Wassilkowa, government of St. Petersburg. 



tischport, Esthonia. Rare in the Echinospherites limestone (CI), 4 

 miles east of Reval. 



Plesioty pes. —C&t. Nos. 57397 to 57402, U.S.N.M. 



British Museum, specimens and thin sections from the Glauconite 

 limestone, Tswos. 



