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BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



massive species with complete diaphragms, Hallopora dyhowskii is 

 very similar in many respects, but its zocecial tubes contain so few 

 diaphragms that they often appear to be wanting. The other species 

 have noticeably smaller zooecia as well as other differences, while 

 associated hemispheric forms of other genera have very distinct 

 internal characters. 



Occurrence. — Nicholson's type-specimens of Diplotrypa petropolitana 

 were collected in the Ordovician (Chasmops) limestone in Ostrogothia, 

 Sweden. Typical specimens from the same limestone at Rabeck, 



d 

 c 



1 



Fig. 195.— Diplotrypa petkopolitana. a, vertical section, x8, of a specimen showing numerous 



CUEA'ED diaphragms; 6, PORTION OF THE SAME SECTION, X20, WITH FUNNEL-SHAPED DIAPHRAGMS IN ONE 

 OP THE ZOCECIAL TUBES; C, ANOTHER PORTION, X20, SHOWING A FEW CTSTIPHRAGM-LIKE STRUCTURES; 

 d, VERTICAL SECTION, X20, THROUGH A MACULA; e, A TANGENTIAL SECTION, X20, SHOWING THE USUAL 

 ARRANGEMENT AND SHAPE OF ZOCECIA AND MESOPORES. LTCKHOLM LIMESTONE (Fl), KERTEL, ISLAND 



OF Dago, Esthonia. 



island of Oeland, are in the collections of the United States National 

 Museum and the British Museum. 



In Russia the species occurs in all the strata ranging from the Glau- 

 conite limestone (B2) to the lower part of the Lyckholm (Fl). The 

 more important localities represented by specimens in the collections 

 of the United States National Museum are: Glauconite limestone 

 (B2), Echinospherites limestone (Cl), and Kuckers shale (C2), Reval, 

 Esthonia; Kuckers shale (C2), Erras, and Baron Toll's estate, 



