CHONETES OP THE CHEMUNG GROUP. 
14a 
netes logani, which I have shown to occur in the Tully limestone of New- 
York; and although distinct species, are not in themselves evidence of 
a higher geological position. 
From the fact that the three species first indicated have this great 
vertical range, we might infer that they would also show a wide geogra¬ 
phical range; but this does not seem to hold true regarding them, in the 
line of exploration which has been followed. 
The Chonetes coronata which is known in Eastern, Central and Western 
New-York in the Hamilton group, is also known in the same horizon in 
Illinois and Iowa ; but it has not been recognized in the Chemung group 
of New-York, Pennsylvania or Ohio, nor elsewhere in that horizon. 
If we regard the Chonetes pusilla as a variety of C. laticosta or C. defteda, 
that species has a wide geographical range, since it occurs on the Missis¬ 
sippi river in Illinois; but it has not been found in New-York or else¬ 
where above the horizon of the Hamilton group. On the other hand, the 
C. logani , which begins its existence in the Tully limestone or the upper 
limit of the Hamilton group, ranges on the west to the base of the Car¬ 
boniferous limestone, though unknown in the Chemung group of New- 
York. 
I may, in the subsequent pages, call attention to other similar examples, in 
reference to geological and geographical distribution of species. 
Chonetes scitula. 
PLATE XXII. 
[ Reference page 130 of this volume.] 
This species, in the shaly beds, preserves impressions of the exterior 
and casts of the interior, showing the characteristic surface markings, the 
spines of the area margin, etc. 
In the coarser sandstones it is somewhat larger and coarser in its mark¬ 
ings; and sometimes the striae are nearly equal, presenting a character 
of surface observed in the Hamilton group. 
The casts of the ventral valve show the filling of the minute tubes 
which correspond to those seen in the shell of the specimens from the 
Hamilton group. 
