teriorly with respect to a line drawn perpendicular to the dentary.
The posterointernal ramal fossa (see Hibbard, 1953) is deeply excavated
with a distinct superior border approximately halfway between its
inferior border and the top of the coronoid. In addition to the
mandibular foramen there is a small foramen immediately posterior to it
opening into the posterointernal ramal fossa. I shall refer to this as
the post-mandibular foramen. The tip of the coronoid is broad, not
tapering, and quadrate, and its entire superior border is inclined
rather sharply medially. Specimen "B" differs from No. 3943 in that the
posterointernal ramal fossa extends nearly to the tip of the coronoid,
which is narrower toward the tip and somewhat tapered dorsally. The
post-mandibular foramen is large and the opening of the mandibular
canal is within the posterointernal ramal fossa. In addition the
coronoid does not incline anteriorly. Specimen "A" is intermediate
between No. 3943 and "B" in the characters mentioned and differs from
both in that the post-mandibular foramen is widely separated from the
mandibular foramen.

Comparison of the Pleistocene specimens with specimens of Recent
species of North American _Sorex_ reveals that the presence or absence
of the post-mandibular foramen is almost constant in any one species.
In possessing this foramen the fossils differ from most individuals of
the species: _Sorex cinereus_, _S. pacificus_, _S. milleri_, _S.
vagrans_, _S. obscurus_, _S. ornatus_, _S. fumeus_, _S. palustris_, _S.
bendirii_, and _S. veraepacis_. The fossils differ from all these
species in other characters as well; consequently detailed comparisons
with them need not be made here. Species which possess the
post-mandibular foramen include _Sorex saussurei_, _S. merriami_, _S.
trowbridgii_, _S. arcticus_, _S. tundrensis_, and _S. sclateri_. _Sorex
merriami_ differs in smaller size, smaller and weaker dentition,
relatively higher coronoid, and relatively deeper and shorter dentary.
_Sorex trowbridgii_ is similar to the fossils and to _S. saussurei_.
Differences between the jaws of _S. trowbridgii_ and _S. saussurei_
seem to me to be differences of size only. _Sorex sclateri_ is larger
than the fossils and m2 is longer in relation to m1, being almost the
same size as m1. In the fossils m2 is noticeably shorter than m1, owing
to close appression of the hypoconid and protoconid and in general to a
smaller talonid area. _Sorex arcticu