228 bulletin: museum of comparative zoology. 



Ruedemann (115) has summarized all that is known about its 

 occurrence in this country, and he, Matthew (104), and Hahn (103), 

 have pointed out the similarity of development of subzones at St. 

 John, New Brunswick, and Scandinavia. Present evidence indicates 

 that the Didyoncma flaheUijormc fauna is the oldest of the Ordovi- 

 cian faunas in both Europe and America, though there is a possibility 

 that the strata with the Acerocare fauna in Scania and the Xiobe 

 fauna in Wales may have to be added to the Ordovician series. 



Brogger (99), attempted a correlation of the Ceratopyge zone wath 

 certain strata in America but though his paper was extremely sug- 

 gestive, no very definite correlations were at the time possible. And 

 even now, we know no typically developed Ceratopyge fauna in 

 America. Walcott (120) has described a trilobite from the lower part 

 of the Goodsir formation of British Columbia as Ceratopyge canadensis, 

 and though it seems very doubtful if this is a Ceratopyge, it probably 

 belongs to the Tremadoc fauna. The writer has described from the 

 same region Hemigyraspis mcconnelli (110), a form indicative of the 

 Asaphellus beds of the Tremadoc of Wales. I have also described, 

 from the Tribes Hill of New York and the equivalent Stonehenge of 

 Pennsylvania, species of Hemigyraspis and Symphysurus also indica- 

 tive of the Ceratopyge fauna. This latter correlation is of considerable 

 importance, for the Stonehenge is the lower member of the Beekman- 

 town in western Central Pennsylvania. The Hemigyraspis fauna 

 occurs in the upper twenty-seven feet of the Stonehenge, which has a 

 thickness of 662 feet, and above the Stonehenge are 2570 feet of strata 

 before the top of the Beekmantown is reached. In the lower Stone- 

 henge, a Dictyonema has been found (Hahn, 103). 



In Russia the Ceratopyge zone is probably not represented. There 

 is of course a temptation to make the Glauconite sandstone the equiva- 

 lent of the whole Ceratopyge zone, especially as one sees in Sweden 

 glauconitic sands associated with the Ceratopyge limestone. In 

 Dalecarlia there is a glauconite sand beneath the Ceratopyge limestone, 

 but in Gastrikland, where the section is very like the Russian section, 

 there is a glauconitic sand above the Ceratopyge limestone, and it 

 seems very probable that this sand is an extension of that so well 

 developed in Esthonia. It seems to belong with the Limbata lime- 

 stone above. This sandstone is thickest in Esthonia, and probably 

 indicates an emergence in that district so that there was some erosion, 

 perhaps accounting for the absence of the Dictyonema shale at Narw^a, 

 and shore or shallow water conditions in Esthonia during the deposi- 

 tion of the Lower Didymograptus shales in Scandinavia. 



