_Eutamias minimus_ the tip of the baculum is longer in
relation to the length of the shaft than it is in adults; the tip is 18
to 28 per cent of the length of the shaft in adults, as opposed to 29 to
32 per cent in juveniles.

_Aberrations._--In a small percentage of specimens of _E. minimus_ and
_E. umbrinus_ the baculum is small and S-shaped, even in adults.

_Variations of taxonomic worth._--Variations in this category are
described in the section immediately following the key.

KEY TO THE BACULA IN EUTAMIAS OF WESTERN NORTH AMERICA

1. Distal 1/2 to 2/3 of shaft markedly compressed laterally; base
markedly widened.

2. Distal 1/2 of shaft laterally compressed and curved downward
to base of tip.

3. Height of keel 1/2 of length of tip; keel markedly
enlarged. _Eutamias bulleri_, p. 627

3'. Height of keel 1/4 of length of tip; keel not markedly
enlarged.
_Eutamias umbrinus_ and _E. palmeri_, pp. 626, 627

2'. Distal 2/3 of shaft laterally compressed and curved downward
to base of tip.

4. Base of keel 1/3 of length of tip; angle formed by tip
and shaft less than 100 deg. _Eutamias speciosus_, p. 625

4'. Base of keel 1/2 of length of tip; angle formed by tip
and shaft more than 102 deg. _Eutamias panamintinus_, p. 625

1'. Distal 1/12 to 2/5 of shaft slightly compressed laterally; base
not markedly widened.

5. Shaft thin; shaft less than .20 mm. in diameter at widest
point.

6. Ridges on either side of keel enlarged, partially
obscuring lateral view of keel; height of keel 1/10 of
length of tip. _Eutamias sonomae_, p. 619

6'. Ridges on either side of tip not enlarged, not partially
obscuring lateral view of keel; height of keel at least
1/7 of length of tip.

7. Base not widened or dorsoventrally thickened.

8. Shaft more than 4.5 mm. in length; tip 16 per
cent of length of shaft; shaft strongly incised
on dorsal side of base
_Eutamias merriami_, p. 621

8'. Shaft less than 4.4 mm. in length; tip more than
25 per cent of length of shaft; shaft not incised
on d