26 ' NEW YORK STATE MUSEUM 



These nodules contain fossils with their exterior ornament finely 

 retained, that is, replaced in amorphous silica, while in the dolomite 

 the shell substance has been removed and never replaced. The 

 source of the silica here, as in the like segregations associated 

 with limestone, \s probably to be found in the spicules of sponges. 



It will tlius be seen that with the increasing salinity, the Lock- 

 port fauna gave way to the Guelph fauna. At first this condition 

 was only temporary and the Lockport fauna under normal con- 

 ditions once more establishes itself, but is finally displaced by 

 the Guelph fauna which in turn disappears with the formation of the 

 Salina sea. 



The Guelph fauna as a whole presents two distinct types of 

 structure, in that the shells are either large and heavy-shelled or 

 small and thin-shelled. The first of these may be regarded as liv- 

 ing on the exposed edges of the coral reefs and the second in the 

 sheltered places among the coral reefs. It may also be stated that 

 the Lockport and Rochester forms found in the Guelph mostly 

 belong to the smaller type. 



The following is a list of Guelph^ species which have been found 

 in the vicinity of Rochester. Those marked with an asterisk are 

 also found lower in the Niagaran of New York. 



Corals 



Zaphrentis c/. racinensis Whitfield *F. gothlandicus Lambe 



*Enterolasma cf. caliculus Hall F. forbesi Edwards ^ Hainie 



* Diplophyllum caespitosum ^a// *Halysites catenularius Linne 

 Heliophyllum sp. * H. agglomeratus Hall 



* Favosites niagarensis Hall Stromatopora galtensis Z)rt;■^i/J•f/^ 



F. hisingeri Edwaj'ds of Hainie Clathrodictyum ostiolatum Nicholson 



Brachiopods 



Crania sp. C. ? indianensis Hall 



* Dalmanella cf. elegantula Daluian *Spirifer crispus Hisinger 



* Rhipidomella r/. hybrida So-cuej-hy * Whitfieldella nitida Hall 



* Camarotoechia ? neglecta Hall 



Pelecypods 



Mytilarca eduliformis Cla^-ke csf Rtiede- Pterinea subplana Hall 

 maun Conocardium sp. 



Gastropods 



Trematonotus alpheus Hall Poleumita scamnata Clarke cr' Rticde- 



Diaphorostoma niagaren.se Hall niaiin 



I All the species of the Giieloh of New York have been described and illustrated by Clarke 

 and Ruedemann in Memoir 5 of the New York State Museum. 



