wilmams] FAUNAL DISSECTION OF THE DEVONIAN. 71 
enable one familiar with the fossils to distinguish the Ithaca varieties 
from the typical Hamilton species. 
FAUNA OF EASTERN EXTENSION OF PORTAGE FORMATION. 
The identification of the Portage formation in eastern New York 
and Pennsylvania is fairly satisfactory in case the identification refers 
to a recognition of the formation in its eastern extension, irrespective 
of exact equivalency of faunas or likeness of sediments. But in the 
eastern counties neither is it stratigraphically clearly to be distin- 
guished from lower or higher strata, nor does it contain in its fauna 
any characteristic species of the Ithaca expression of the lower Port- 
age formation. Nevertheless, the identification of the strata as the 
outcroppings of the same rocks which farther west are distinguished, 
both lithologically and paleontologically, as lower Portage is well 
demonstrated ; and the assignment on a geological map of the Portage 
color to the region from which the 15 reported faun ales came is 
defensible, if it be granted that the same formation name may be 
applied to strata of which the contemporaneous sedimentation can be 
established, although their lithological and paleontological characters 
are different. 
I take this case from the region holding the typical Hamilton for- 
mation, with its Tropidoleptus carinatus fauna, to illustrate a phase 
of a fauna which is, without question, directly descended from the 
typical Tropidoleptus fauna, but is certainly younger. 
How is such a fauna distinguished? 
(1) The great majority of its species are the same as those of the 
typical Tropidoleptus carinatus fauna below. 
(2) The few distinctive species never appear at the lower horizon, 
but they are frequent above, and first appear at a like horizon over 
considerable area; and 
(3) They are more prominent in frequency of individuals where the 
characteristic species of the Tropidoleptus carinatus fauna are deficient. 
In the 15 faunule lists of this group given by Prosser, 41 species are 
positively identified. 
Of these 41 species, 34 are recurrent species, and among the domi- 
nant species of the Portage fauna occur five species and two varie- 
ties of the Tropidoleptus fauna. 
Of the standard Tropidoleptus carinatus list, six species are reported 
the number of times, out of a possible 15 localities, indicated by the 
figures in the following list: 
Table X.—Becurren t species of the Tropidoleptus fauna in the Portage formal ion . 
Tropidoleptus carinatus - - 8 
Nucula corbulif ormis - - 3 
Pala?oneilo constricta 3 
Nuculites oblongatus '•> 
Phacops rana - - - - - - - 1 
Spirifer (mucronatus) pennatus - - - - - 1 
