Williams.] FAUNAL DISSECTION OF THE DEVONIAN. 69 
in which the}' occur, may be interpreted as indicating modification 
of the fauna as a whole, due either to lapse of time in the same region, 
resulting in the loss of supremacy of these species, or to shifting of 
the fauna as a whole, resulting in loss of life and change in the 
equilibrium of the species owing to change of conditions of life. 
It will be remembered that in the section running through Cayuga 
Lake and Ithaca, which was elaborated in 1883, a both the Tully lime- 
stone and the Genesee shales are distinct formations and form a 
definite termination for the Hamilton formation. 
It was pointed out in a later paper h that this zone was indicated by 
the first appearance in the New York section of Rhy nchonella (Hypo- 
thyris) cuboides (=R. venustula Hall) and other species not found 
below in the Hamilton, but widely distributed in other parts of 
the world. The inference was drawn that there had been modifica- 
tion of the local fauna by immigration of foreign elements. The 
fauna to which these immigrants belonged in other regions was 
observed to be more intimately associated with the later faunas of 
the New York region (the Spirifer disjunctus fauna) than with the 
Tropidoleptus fauna, and the conclusion was therefore reached that 
the Tully limestone was more naturally associated faunally with the 
formations that stratigraphically follow it than with the Tropidoleptus 
carinatus fauna of the Hamilton, and so, in spite of the survival of 
many species of the underlying formation, the fauna of the Tully 
limestone was appropriately called the cuboides fauna, from the 
dominance of this new form, Rhynchonella cuboides. 
In the more exact nomenclature adopted in writing this paper the 
cuboides fauna may be regarded as only a faunule — that is, only a 
local and temporary representative of a fauna which, though not 
widely represented in the interior continental basin of North America, 
probably had its fuller characteristics expressed in the outer Manitoba- 
Mackenzie River seas of Devonian time. 
In the Cayuga Lake-Ithaca section, above the Tulty came the black 
Genesee shale with its Lingula spatidata faunule. e This faunule 
contains Amboccdia umbonata, but no other one of the 12 dominant 
species of the Tropidoleptus fauna. Following this was a small 
faunule which is related to the Portage fauna of the Genesee Valley, 
as seen by the continued presence of Cardiola speciosa; (l and above 
that came the Spirifer Ice/vis faunule, still a modification of the western 
Cardiola (Portage) fauna/ but mingled with some of the species of 
the Tropidoleptus fauna. Still a third modification of the Cardiola 
fauna is seen in some black or dark shales above the Spirifer l&vis 
«Onthe fossil faunas of the Upper Devonian along the meridian of 76° 30 7 from Tompkins 
County, N. Y., to Bradford County, Pa., by H. S. Williams: Bull. U. S. Geol. Survey No. 3. 
?>Tho Cuboides zone and its fauna; a discussion of methods of correlation, by H. S. Williams: 
Bull. Geol. Soc. Am., Vol. I, pp. 481-501, Pis. XI-XIII. 
(•Bull. U. S. Geol. Survey No. 3, p. 9. 
d Ibid., p. 11. 
<-Ibid., p. 12. 
