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jahnsi. This method for graphical representation of size
differences is taken from G. G. Simpson (1941) which includes
a complete explanation of the construction and interpreta-
tion of this figure. The method essentially compares the
relative proportions of dimensions in any number of different
species (three in this case) to a single form arbitrarily
picked as the standard of comparison,!::!• (Merychyus) crabilli
in this case. The dimensions are converted to a geometric
or logarithmic scale in order that an absolute ratio of
numbers will be represented by the same distance plotted on
the graph. Since we desire to ignore absolute values and
represent only ratios, the differences between logarithms
are plotted. The log difference scale is plotted on the
ordinate and the various dimensions on the abscissa. Negative
log difference·values represent a ratio which is less than
one, or in other words, a ratio in which the standard of
comparison is larger than the form to which it is being com-
pared. The horizontal lines plotted along the ordinate
at each character are a log measure of the estimated range
of that character. This estimate was obtained by taking
3.24 times the standard deviation (see Simpson, et al.,
1960). The small number indicates the sample size.-Figure 2
reveals that!::!• (!::!.) jahnsi is consistently smaller than!::!•
(!::!•) crabilli, well outside of the estimated maximum vari-
ability found in the latter. However, at least in relation
to the proportion of the characters compared, !::!• (!::!.) j ahns i
displays a close resemblance to!'.!• (!'.!.) calaminthus. The
·presence of long shallow antorbital fossae, paired infra-
orbital foramina, a relatively shallower malar and a relative-
ly smaller M 1 serves to distinguish further !'.!• (!'.!•) jahnsi
from !'.!• (!'.! •) calamin thus.

PHYLOGENETIC POSITION OF THE TICK CANYON OREODONTS

There are a number of unpublished oreodont records from
Southern California which yield pertinent information about
the phylogenetic position of the Tick Canyon oreodonts. The
Hemingfordian Boron fauna (Whistler, University of California,
Riverside, Master's thesis, 1964) contains two well repre-
sented species of Merychyus which display affinities with
M. (M.) calaminthus and M. (M.) jahnsi. Both an unpublished
Arikareean fauna in the Mojave Desert and the Hemingfordian

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