334 Cincinnati Society of Natural History. 
the practical observations of careful persons in working up many of 
the mysteries clinging to varieties and their causes. 
To this end such papers as this may contribute a feeble mite. Laws 
as yet poorly understood underlie these varieties, and the frequently un- 
explained mystery of their distribution and association. To the sin- 
cere student of this subject these are the topics of highest consequence, 
because they point out the phylogenic line along which we may hope 
to trace some of the questions of descent. The molluscan tribes now 
inhabiting the globe are only the modified remnants of ancestral lines, 
extending back into the previous ages, and having, no doubt, numer- 
ous breaks and changes that might be explained by reference to well 
understood present laws of life. But how rare the cases in which we 
have even crossed the threshold of this domain, to say nothing of our 
absolute want of common knowledge with regard to the rarer vital 
phenomena common to all animal life. To this end one suggestion, 
_ which I do not remember to have seen publicly made, occurs to me 
here. That all collectors and students of shells, in regions where Post- 
pliocene species can be obtained, or species from the Loess, especially 
of the Mississippi Valley, and from dried up lakes, Tertiary basins, 
etc., make every effort to gather together this material, and to com- 
pare notes upon the same. A dead snail, from under an old log or 
stump is perfectly worthless when abundance of living ones can be had; 
but a dead shell from a lacustrine or fluviatile deposit, having a greater 
or less antiquity, is quite another thing, and may teach a lesson of 
very high value. A correspondent sent me for a long time only dead 
shells of the Helicina occulta. Finally specimens occurred among 
them so little damaged, that I suggested to him the probability that 
close search would reveal the living ones. His efforts were successful, 
now another correspondent sends me thirty or forty living specimens, 
years after, from a near locality, and among the variety H. rubella, 
Say. Among a lot of dead Succineas, quite worthless to the general 
observer, I found a type of the rare S. hawkinsii, Baird. Since 
then I have been willing to carefully examine, for my correspond- 
ent, any such material, in the hope of finding some key to lost or ob- 
scure species, to varieties and their causes, and especially to learn, by 
actual comparison, the changes which species have undergone during 
long periods of time. Ifthe collector who undertakes this work, will 
assiduously apply. himself to the study of the circumstances of the de- 
- posit, and the age of the formation in which his shells occur, and if he 
has not the necessary knowledge, hooks of reference and other con- 
) ele tia tare 7 
" 4, 
4 
