﻿198 H. S. Williams — Lamellibranchiata and Species-making. 



are the Monoinyaria, which are less abundant in the eastern 

 sections. The Ithaca group of Lamellibranchs are more closely 

 allied with the Hamilton than with the Chemung forms. 



The species and even the genera of Lamellibranchs, as here 

 represented, appear to be much more sensitive to conditions of 

 environment than are the Brachiopods, as shown by the associa- 

 tion of certain species and genera with particular kinds of deposit. 

 The fauna of the coarser sands toward the termination of the 

 Chemung period presents a clearly defined set of Lamelli- 

 branchs, — as the Palceanatinas, the u Ptychopterias" certain of 

 the Orammysias and Sanguinoliies= il Sphenotus" 



In his remarks upon the classification of the rocks of the 

 Devonian, Professor Hall appears rather to add to the confusion 

 than alleviate it. The Oneonta reds and grays, although litho- 

 logically indistinguishable from genuine Catskill rocks, and 

 containing unmistakable Bothriolepis scales (a genus hitherto 

 regarded as characteristic of the Catskill deposits), is distin- 

 guished from it, "and forms no part of the Catskill group" 

 (p. 518). 



It is stated (p. xix) that u it has not been shown that " [the 

 Ithaca] " formation is distinctly separated from the typical 

 Chemung lying above," and, I suppose, it is for this reason that 

 on page 538 we find the note that " The Chemung group is here 

 intended to include all the strata between the Catskill and Por- 

 tage groups. In this volume the strata at Ithaca have been 

 referred to the lower portion of the Chemung group." The 

 facts are that the fossiliferous zone at Ithaca is separated from 

 the lowest beds containing characteristic Chemung fossils by 

 about six hundred feet of nearly barren, flaggy and shaly deposits, 

 but with a few fossils which belong to the characteristic Portage 

 fauna. Also the Oneonta rocks, going westward, gradually merge 

 into the rocks which at Ithaca contain the fossiliferous beds, 

 but on page 517 it is said " this portion of the series apparently 

 merges into succeeding Portage groups of which further west 

 it forms a part." 



There is here some confusion. Although it would be dif- 

 ficult to distribute in a continuous column the several distinct 

 local representatives of the upper Devonian for New York and 

 Pennsylvania, it is unfortunate to throw together species of 

 two zones so distinct as those at Ithaca and the typical Chemung 

 zones higher up. The Ithaca fauna and its equivalents are 

 wanting in the more characteristic of the Chemung species, and 

 its whole facies links it as intimately with the Hamilton as with 

 the typical Chemung fauna. 



Ithaca, N. T., April 2*7, 1886. 



