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Ra Observations on the Unification of Geological Nomenclature. 281 
Among the Brachiopoda, Rhynchonella occurs in nearly every group 
to modern time. 
Among the Gasteropoda, Capulus extends to the Coal Measures; 
Bucania to the Lower Helderberg; Raphistoma to the Niagara; and 
Scalites to the Trenton. 
Among the Cephalopoda, Actinoceras extends to the Carboniferous; 
Oncoceras to the Niagara; and Ormoceras to the Clinton. 
Among the Lamellibranchiata, Modiolopsis to the Lower Helderberg; 
and Ambonychia to the Niagara. 
Among the Crustacea, Spherexochus occurs in the Black River and 
_ Niagara Groups. 
Of the 24 genera that come into an existence in this group, five do 
not pass beyond it; four terminate in groups belonging to the Lower 
Silurian; nine in the Upper Silurian; one in the Devonian; four in the 
Carboniferous; and one has existed through all succeeding time. 
This group not only graduates lithologically into the Black River, but 
it is connected intimately by numerous species, some of which pass into 
the Trenton and Hudson River Groups. Strophomena alternata, and 
S. tncrassata, pass up into the Hudson River; and Orthis borealis, O, 
disparilis, O. perveta, Leperditia canadensis, L. louckana, L. amygda- 
dina, Orthoceras multicameratum, O. bilineatum, Modiolopsis nasuta, 
are among those that pass up into the Trenton Group. The separation 
from the Black River is however very marked where the passage beds 
formed by the Birdseye limestone do not intervene. 
The Black River Group.—This Group was defined by Lardner Van- 
uxem in 1842, and named from Black River, New York. It includes 
the Birdseye and Black River limestones. The Birdseye received its 
name from the crystalline spots of a species of Tetradium, and a fucoid, 
which areshown when the rock is fractured. It is distinguished by its 
_ light dove color, thick layers, and vertical joints. It is foand in Essex, 
Clinton, Lewis, and Jefferson counties, New York, having a thickness 
of 30 feet. It has been identified in a few other places in the State 
and alsoin Vermont, but in Canada it has become so united with other 
strata, that no line of separation can be determined. 
Phytopsis, Stromatocerium, Tetradium, Orthostoma, and Colpoceras 
are genera that appear for the first time in the Birdseye limestone, but 
all of them occur in the Black River limestone, Colpoceras occurs also 
in the Trenton, and Tetradium in the Trenton and Hudson River, and 
as so many species range into the Black River limestone, there is not 
sufficient reason for ranking it higher than beds of passage forming 
the lower part of the Black River Group. 
