478 EDWARD L. TROXELL 
tend to separate two groups, based on our general conception of 
the ultimate barrier between species. 
Carrying the subject to a further quantitative analysis, what 
range of “‘ratios” can we allow within a species? Two skulls of 
approximately the same size may vary in proportions, one part 
being r5 per cent larger, another part as much smaller. Here is a 
range of 30 per cent; is it a specific difference? The personal 
equation of course enters into all such questions and the resulting 
taxonomy. 
Presenting specific characters.—A glance through the literature 
shows many instances where an author at the beginning of an 
original description states that the “specific characters” are so 
and so, and proceeds to list a number of features which, taken 
singly, might not even be subspecific, or, on the other hand, might 
be generic. In addition, these “specific characters” which may 
serve to distinguish two species do not show a contrast with a third 
or fourth; for instance, characters “‘a’’ may show the distinction 
from species ‘‘A,” but we must look for another group of criteria, 
““b,”? to separate our species from ““B.” A species depends not 
only upon its own features as selected by its author, but upon the 
features of the other species in the genus as well; the specific 
characters marking the boundary in one direction may not be such 
as to show it in another. 
New discoveries are constantly being made which contradict 
general statements of distinctions, and overturn our nicely adjusted 
taxonomy, unless we carefully indicate the type material compared 
when we draw our contrasts. The safer course, then, seems to be 
to limit one’s self to the “distinguishing characters,” as so many 
paleontologists do, without making a guess as to what the undis- 
covered or unknown specimens may show; or to indicate just 
what species are being distinguished by certain characters, in 
which case the description resolves itself into as many parts as 
there ‘are species to be compared, and each description shows 
definite contrasts and possibly a wholly different set of distinguish- 
ing features; all of this is again subject to one’s learning and powers 
of contrasting the variables. 
