ITHACA FAUi^A 



445 



Hamilton species could invade the Ithaca region while the new formed 

 species of that province spread eastward into the area formerly held by 

 a pure Hamilton fauna. This mixed fauna is the Ithaca fauna, and 

 that it is composed of the mingling of the pure Hamilton fauna from the 

 east and the provincialized and modified Hamilton fauna from the Ithaca 

 region is seen in the preponderance of the latter type of species in the 

 Ithaca fauna of the t3^pe region and of the Hamilton species in the Ithaca 

 fauna of the east. 



The Ithaca Fauna 



The Ithaca beds and fauna were first named by H. S. Williams from 

 the occurrence of this fauna above the Lower Portage (Sherburne) in the 

 Ithaca region. It was a fortunate coincidence that the fauna was named 

 from this region, since its distinctive species developed here, as first 

 pointed out by Dr. J. M. Clarke, occupying at first in their purity the 

 Sherburne or Lower Portage beds. Then the Ithaca congeries was 

 formed by the commingling of this fauna with the Hamilton fauna from 

 the east. The Ithaca fauna ranges here through a considerable thickness 

 of strata and is finally replaced by the Chemung fauna. Westward, as 

 shown by John M. Clarke, the corresponding Portage beds carry the 

 N'aples fauna, from which Ithaca species are, however, excluded. 



A study of the table on page 437 brings out the following facts: Of 

 the 124 forms listed, 7 are not specifically identified, leaving 117 species. 

 Of these 10 are doubtful, 6 being Hamilton forms. There thus remain 

 107 identified species from the Ithaca formation of Ithaca. Of these 

 30, or 36.45 per cent are Hamilton species, 12 are Naples species, but 3 

 of these are also Hamilton forms, leaving 9, or 8.41 per cent, added from 

 the Naples fauna. Finally, there are 3 pure lowan types. This makes 

 a total of 51 "foreign" species in the Ithaca, leaving 56 indigenous ones. 

 Of these 18 occur in the Lower Portage or Sherburne of the' Ithaca 

 region, leaving 38 new forms not yet accounted for. When compared 

 with the Hamilton species, nearly all can be recognized as derivatives 

 from that fauna, as was the case with the modified species of the under- 

 lying Sherburne. In the following list it is attempted to refer these 

 species to their nearest Hamilton relative. 



Brachiopoda 

 10. Camarotoe cilia contracta Hall 



There are several Hamilton species from which this could be 

 derived. Possibly C. dotis most nearly fulfills the requirements 

 for an ancestor. 



