EAELY PALEOZOIC BEYOZOA OP THE BALTIC PROVINCES. 265 



extends almost across the cell cavity is apparent in tangential sec- 

 tions from the small opening left on one side. From the small size 

 of this curved portion it is also evident that the diaphragms extend 

 almost entirely around the zooecial cavity. 



Occun^ence. — Not uncommon in the Echinospherites limestone (Cl) 

 at Reval and 4 miles east of Reval, in Esthonia, and at Katlino and 

 Duboviki in the government of St. Petersburg; in the Kuckers shale 

 (C2), Baron Toll's estate, near Jewe. The species also occurs in the 

 Chasmops Hmestone on the island of Oeland, south of Bodahamn. 

 (Cat. Nos. 57366 to 57370). 



British Museum, specimens from the island of Oeland. 



Division INTEGRATA XTlrich and Bassler. 



Family AMPLEXOPORIDvE Ulrich. 



The simplest types of the Integrata are included in this family, 

 which, because of this simplicity as well as the practical absence of 

 mesopores, shows the duplex character of the walls most distinctly. 

 In the HaUoporidse and Trematoporidse mesopores are almost inva- 

 riably present, and the black divisional line is then only apparent 

 where the zooecial walls are in contact. 



The Amplexoporidse include forms of a ramose, massive, or bifohate 

 growth. The zooecial tubes are simple, polygonal, with a distinct 

 divisional line. Mesopores are practically wanting, a few abortive 

 cells in the maculae being their only representatives. Acanthopores 

 are generally abundant, although sometimes wantmg. 



The type genus of the family, Amplexopora, has no known repre- 

 sentation in the Ordovician of Russia or in the Black River deposits 

 of America. It is abundantly represented in the upper Trenton and 

 Cincinnatian formations of the Mississippi Valley. MonotrypeUa like- 

 wise occurs only in the formations containing faunas of supposed 

 South Atlantic origin. RhombotryjM is found only in the earliest 

 Silurian deposits, where its several species are highly diagnostic fossils. 

 I am convinced that further search will show this genus to be repre- 

 sented in the upper Lyckholm and BorkhoLm, where species asso- 

 ciated with it in America are known. 



The discovery of a typical species of Petalotrypa in the Middle 

 Ordovician rocks of Russia increases the geologic range of the genus. 

 Hitherto it has been considered typical of the upper part of the 

 Silurian and of the DeA'onian. 



Genus PETALOTRYPA Ulrieh. 



Petalotrypa Ulrich, Geol. Surv. Illinois, vol. 8, 1890, pp. 377, 453. — Simpson, 

 Fourteenth Ann. Rep. State Geologist of New York for the year 1894, 1897, 

 p. 582.— NiCKLES and Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 30. 



Amplexoporidfe in which the zoarium forms delicate, bifoliate, 

 thin branches or fronds. The zooecial structure is essentially as in 

 other genera of the family; that is, the walls of adjoining cells are 



