SILURIC FAUNA FROM SOUTHERN MICHIGAN 551 



Cephalopoda : 



11. 7'rochoceras (Mitroceras) ijehlmnli Hall. 



OSTRACODA : 



12. Leperditia scalaris Jones ; common. 



Plants : , 



13. Nematophytum crassum Penhallow ; rare. 



14. ButhotUrephis clavelloides Grabau manuscript ; rare. 



Schuchertella interstriata, Spirifer eriensis, Mitroceras gehhardi, and Lep- 

 erditia scalaris link this fauna with the Cobleskill. Schuchertella interstriata 

 and the Whitfleldellas link it with the Amherstburg. 



Discussion of the Faunal Differences 



A survey of these faunas brings out the remarkable fact that there is nothing 

 in common (a few doubtfully identified gastropods excepted) between the Lower 

 and Upper Monroe. So distinct are the faunas that they may be considered as 

 derived from widely separated provinces. The Lower Monroe is apparently an 

 Atlantic fauna or series of faunas, and we are led to believe that an embay- 

 ment from the Atlantic extended as far as Wisconsin in post-Salina time, and 

 that the successive members of the Lower Monroe were deposited in this. The 

 marine "Salina" described by Schuchert from Maryland most probably belongs 

 here, the path of invasion being approximately across that region. There ap- 

 pears to be nothing in New York which corresponds to this series, that state 

 being apparently north of the embayment. The embayment covered Ohio. 

 Michigan, and probably a part of Indiana, and extended into Wisconsin. 



Following the deposition of the Lower Monroe came a retreat of the sea and 

 jfiolian deposits of quartz sands accumulated upon the limestone foundation. 

 These are now seen in the Sylvania sandstone, the source of the material of 

 which probably was the Saint Peter sandstone. The Upper Monroe invasion 

 was from the northwest, and it brought with it a wholly new fauna, in which 

 the prevailing element was of Devonic aspect. A large proportion of the spe- 

 cies of the Anderdon and Amherstburg beds is most nearly related to the Scho- 

 harie fauna, the similarity being often so great that species have been de- 

 scribed as Schoharie or Onondaga forms. 



The following are the species more nearly related to mid-Devonic forms than 

 to known Siluric : 



Stromatoporoids : 



1. Stylodictyon sherzeri cf. S. columnare. 



2. Idiostroma nattressi cf. /. traversense Grabau manuscript. 



Anthozoa : 



3. HeUophrentis alteniatiim cf. unidentified Schoharie form. 



4. Mutation compressa and Mut. magna cf. 



5. S. carinata. 



6. Gystiphyllum americanum, Mut. anderdaiieiise cf. C. ameriranum. 



7. Acervularia sp. cf. A. riioosa. 



8. Romingeria iimhillifera, R. umlnUi^era. 



9. Ceratopora regiilaris. 



10. Favosites hasaltica nana cf. F. hasaltica. 



