THE NAUTILUS. 51 
by individual variations (which must usually be quickly effaced by 
interbreeding with normal or differently modified individuals), but 
by the steady action on the entire mass of the factors of climate, 
elevation, food-plants, currents and other quantities of the complex 
equation unknown to us.’ 
Mr. Wetherby proposes to avoid the use of subspecific or varietal 
names by the circuitous method of writing the Jocality after the 
specific name. He would say “ H. tridentata Say, var. Campbell 
Co., Tenn.” “ H. tridentata var. Cincinnati, O.” “ H. cereolus var. 
Sanford, Fla.” ete. Now the disadvantage of this system is that it 
tells absolutely nothing to the man who has no specimens from those 
exact localities, without a detailed description of the shells in each 
ease. Moreover, Mr. Wetherby would write “H. appressa var. 
Woodville, Ala.” for both H. appressa perigrapta and H. sargent- 
dana, two very dissimilar forms. Who would know which one he 
meant to indicate? The trinomial system on the other hand offers 
a convenient, concise, readily understood index to geographic and 
local races. When one says “P. cereolus septemvolva” the idea is con- 
veyed as exactly and much more concisely than by saying “ P. 
cereolus large var. St. Augustine,” for unless one has specimens from 
this locality he would not then know just what was meant. Again, 
were one to say “ P. cereolus small var. Sanford, Fla.” nobody could 
tell whether the variety found there was that with an internal lamina 
(P. cereolus carpenteriana) or without a lamina (P. cereolus volvowis). 
Now what is the use in all this cireumlocution when we have so 
convenient a system of nomenclature as the trinomial system, 
already in practical use in other departments of zoology. 
Having discussed the abstract questions at issue at such length, 
we can devote but little space to the particular cases cited by Mr. 
Wetherby ; but this is the less needful because what we wish to estab- 
lish is the great importance of subspecies in general, not of any partic- 
ular one of our own naming. We may, however, re-affirm the 
3One of the most potent causes of specific or varietal differentiation has 
been the glacial epoch, which undoubtedly caused a southward movement of 
the entire northern fauna. Upon the recession of the ice sheet the species 
thus driven south found themselves exposed to changing climate and food- 
plants in their new home. Those following the retreat of the ice found the 
topography, soil and drainage systems of their former area in the north vastly 
changed. What wonder that we find many geographic subspecies! And shall 
we shut our eyes to the results upon our snails of the action of these cosmic 
forces, these manifestations of the Omnipotent ? 
