108 HENRY SHALER WILLIAMS 
of report of the species from rocks believed to be of a lower horizon 
than Chemung, but in several doubtful cases of this kind investigation 
has shown the absence of any conclusive evidence that the species was 
actually derived from the horizons mentioned. In all cases in which 
the evidence is at hand for critical study no fauna containing authentic 
specimens of S‘pirifer disjunctus has been seen in New York or adjoin- 
ing territory which upon any other kind of evidence can be satisfac- 
torily thrown into a stratigraphic horizon below the base of the 
Chemung formation. 
Many other species than those above mentioned have been listed 
from the Chemung formation, and they also may be recognized as 
good Chemung species; but it is important here to determine which 
particular species are diagnostic of the typical Chemung fauna, in 
order to establish an exact standard from which to trace the formation 
beyond the locality of its original definition. 
In drawing the lines for the Watkins Glen quadrangle map the 
base of the Chemung formation has been discriminated by means of 
the above listed species. The formation line is thrown down as 
low as any of these diagnostic species have been certainly detected. 
This line has proven to be drawn consistently with the observed 
stratigraphy and conforms to the structural facts. This revision puts 
the line stratigraphically higher by some two hundred feet than I 
located it in 1884.2, The faunule of Station No. 58 of that paper con- 
tains a species of Productella which I then identified with P. lachry- 
mosa, and also the following species: Ambocoelia umbonata var. 
gregaria, Orthis impressa, and Atrypa reticularis. ‘The faunas listed 
as 62a and 62) contain Lingula complanata and Spirijer (Delthyris) 
mesicostalis. All these are now thrown below the base of the Che- 
mung, because of absence in them of the diagnostic species above 
cited. 
The Van Etten Zone of Tropidoleptus.—The portion of the column 
thus thrown down from the Chemung into the upper part of the Nunda 
t See Prosser, ‘‘The Devonian System of Eastern Pennsylvania and New York,” 
U. S. Geol. Survey, Bull. 120 (1894), p. 12; Also Williams, “‘On the Formational 
Correlation of the Catawissa Section,” in Contributions to Devonian Paleontology, 
U.S. Geol. Survey, Bull. 244, pp. 78 ff., 1905. 
2“ On the Fossil Faunas of the Upper Devonian,” U. S. Geol. Survey, Bull. 3, 
p22t. 
