1885.] in Pennsylvania and New York. 647 
“The other specimen, only a couple of inches distant, has the 
characteristic plications on the medial fold, and with the surface 
equally well preserved, shows not the least nn = radiate or 
Sohne strie, unmistakably indicating S. disjun 
“From the same locality, though not on this individual slab, 
are specimens of both varieties of the so-called S. mesocostalis— 
the large coarse form with angular plications and reduplicated 
fold, and the more finely plicated form with prolonged hinge line 
which is more characteristic of a lower horizon.’ 
From these statements of Professor Williams we find that the 
three following inferences are now known to be true for Mew York 
State: 
1. That S. mesocostalis occurs associated with S. mesostrialis. 
2. That S. mesocostalts occurs associated with S. disjuncta. 
3. That S. mesostrialis occurs associated with S. disjuncta. 
These are all the possible combinations of three things taken 
two together. Consequently these three species are mingled in 
New York State in all possible ways in which two of them can 
be combined. 
In order to strengthen, if possible, by cumulative evidence the 
argument founded on these clear and definite statements, the- 
writer applied to Professor R. P. Whitfield, of New York, asking 
if the collection of the New York Museum of Science, of which ` 
he is curator, could supply any facts that would support the views 
on the range of these fossils which are here maintained. The 
greater part of that collection was made and the specimens 
named by Professor Hall, so that no doubt regarding the identi- 
fication of the species can be entertained. Professor Whitfield 
has stated in reply: 
1. “Ona small block of sandstone containing the specimen of 
S: p ipaairsy figured in the Palæontology of New York (Vol. 
Iv, Pl. xL, Fig. 6), there is an imprint of a part of a very charac- 
me iA of S. disjuncta. 
“ Another specimen measuring four inches by three, from 
Schoharie county, N. Y., and bearing Professor Hall’s ticket (No. 
302), contains one of the specimens of S. mesostrialis, figured in 
the same plate (Pl. xx), and also casts or imprints of three indi- 
viduals of S. mesocostalts, 
3. “ Another small slab marked, in Professor Hall’s writing, 
‘ Tioga county, N. Y.,’ contains two dorsal valves of S. disjuncta 
and two ventrals of S. mesocostatis. 
a antes small block, bearing Professor Hall’s ticket, shows 
dorsal valves of S. mesocostalis with specimens of the long mu- 
cronate hinged form of S. disjuncta. 
