ITHACA FAUXA -141 



In any case, these species — providing their identification is correct, 

 which is at least doubtful in the case of the Modiomorpha — do not offer 

 an}' serious argument against the conclusion that the fauna of the Sher- 

 burne east of the Unadilla and that of the same horizon west of . the 

 Chenango Eiver are distinct, the former remaining a typical Hamilton 

 fauna, the latter becoming a modified fauna, influenced in part by the 

 Naples fauna of the region farther west, of which it contains several of 

 the most characteristic species. Judging from analogy with modern 

 faunas, we may conclude that the eastern region was in constant con- 

 nection with the center of distribution of the Hamilton fauna, and so 

 remained true to type, while the western region was almost entirely cut 

 off from the further immigration of Hamilton types, and so became 

 modified into a provincial fauna. 



The barrier which effected this separation was the non-marine phase of 

 the Sherburne — that is, the typical Sherburne — which is now shown be- 

 tween the Unadilla and Chenango rivers of New York. This appears to 

 have been a low sand bar about 10 miles across, which extended from the 

 mainland to the north as a prolonged bar or sand spit across New York. 

 To the south this bar extended into the region of black mud deposition, 

 which served to complete the barrier." 



This is essentially the bar previously outlined by Dr. John M. Clarke 

 (New York State Museum Memoir 6, Plate A), though he has not at- 

 tempted to show its relationship south of New York State. In early 

 Portage time the eastern area was still connected with the Atlantic by 

 way of the Champlain-Saint Lawrence channel. 



If we now consider the 32 species recorded from the western Sher- 

 burne which are not persistent Hamilton types, we can refer most of 

 them to a probable ancestor in the Hamilton. Two of the corals, Aidopora 

 and CladochonuSj are not specifically identified, and the same is true of 

 one pteropod. Two others are plants which may also occur in the Ham- 

 ilton. This leaves 27 species to be accounted for. They will now be 

 considered seriatim. 



Brachiopoda 

 11. Camarotoechia eximia Hall 



This appears to be a derivative of C. prolifica of the Hamilton, 

 which species the young of the present form resembles. The main 

 difference is in the finer plications of the later species, while the 

 fold and sinus develop at a much later stage. This species ap- 

 parently does not extend beyond the Ithaca beds. 



See map, p. 955, fig. 3, this Bulletin, vol. 28. 



