646 On the Vertical Range of Certain Fossil Species (July, 
coexisting in the same stratum or at the same horizon or outside 
the limits of the typical Chemung. He would not be surprised 
if S. mesocostalis were found to ascend high enough above its 
proper horizon to mingle with S. disjuncta. But he cannot com- 
sae how S, disjuncta and S. mesostrialis should be found to- 
gether. 
In regard to this point the experience of the writer in Penn- 
sylvania has led him to very different conclusions. So far from 
being strictly limited to single horizons, these three species appear 
to range with great latitude over each other's territory. This is 
especially true of the two lower fossils, S. mesocostalis and S. 
mesostrialis, It is no doubt true that each species is specially 
abundant in certain beds or zones, but while in a measure charac- 
terizing these, it spreads both above and below them, and mixes 
with one or both of the others. 
These statements are made concerning Middle Pennsylvania 
and have no reference to any other district. The writer’s expe- 
rience among the rocks and fossils of New York is not sufficient 
to enable him to speak with any authority concerning them, and 
to these it may be supposed Professor Hall is chiefly referring in 
the passage quoted above. 
Since the publication, however, of the report of Professor 
White, and called forth by its preface, a letter has appeared from 
the pen-of Professor H. S. Williams, of Cornell- University, in 
which, referring to these remarks of Professor Hall, he says: 
“While the statement cited may express the general rule as 
to the occurrence of the species in New York State, there are 
specimens in Cornell University museum which do not bear out 
the statement. 
“In the first place the two species, S. mesostrialis and S. meso- 
costalis, are found associated in the same stratum at Ithaca, N. Y., 
both in the mesostrialis zone and in the mesocostalis zone. Sev- 
eral instances can be shown where they occur on the same slab. 
“ From a higher horizon in New York State, and from several 
localities, either of these species may be found associated with S. 
disjuncta, and I have obtained each of the three ney from the 
“representatives of S: notte and S. senses ` the latte tter pre- 
-serving ‘ the fine radiate striæ with delicate concentric crosslines’ 
— without ut a depression’ which are describéd as distinctive charac- 
A T pe (Pal. N. Y., Vol. iv, p. 243). 
