50 THE NAUTILUS. 
were found living in one respect, at least, under a different condi- 
tion. Without entering into a general revision of the North Ameri- 
can Physade, a task which, sooner or later, will be required, I will 
state that I regard P. triticea as simply an immature aspect of the 
almost universally distributed Physa gyrina, and the larger speci- 
mens collected by me at Auburn, though smaller than the average 
of adult gyrina, connect the two. 
The conditions under which the Auburn lots occur are as follows: 
The smaller, which would surely be placed with triticea, were col- 
lected close to springs, where the flow of water at its maximum is 
small, and its catchment is limited and confined in small hollows. 
A part of the year these springs must be quite dry, though most of 
the time yielding a feeble trickling stream. Colonies of Physe 
became established hereabouts, but when mature, attain a size hardly 
equal to that of an ordinary P. gyrina, minus the final whorl, and 
showing the characters that P. gyrina exhibits from the apex down 
to and inclusive of the penultimate whorl. It is an arrested, un- 
developed form, equal to P. gyrina adolescent. The larger Auburn 
specimens, though still exhibiting much of the aspect of triticea, in- 
dicate, as before implied, their relation to gyrina, and were collected 
where the flow of water is generally permanent and the quantity 
much greater than in the other instances, but still where there is 
not even a permanent pool, and no runway of water that could be 
called a permanent brook or streamlet. 
The geological character of the region is a slate that is folded 
and tilted and tipped; it seems much more favorable to the forma- 
tion of small springs than to permanent brooks and flowing 
streams, though the latter are occasionally met with, being fed by 
the melting snows of higher elevations. 
The surface of the pond snails, which authors describe with a 
nicety that would be commendable if it were not so often absurd 
and embarrassing, varies exceedingly in texture, sculpture and color ; 
adolescent individuals of the same species or colony may be pellucid, 
and mature ones opaque; young shells may have a smooth surface, 
and old ones exhibit growth lines; the surface in some may be even, 
in others malleated, and so on; and color is modified if the speci- 
mens, when collected and placed in water, are allowed to remain 
until maceration has reached a putrid stage, when the interior of 
the shell becomes blackened either by the adherence of decayed 
matter or by chemical discoloration; the membranaceous composi- 
