Four specimens of _meridionalis_ trapped in July at the type locality,
only one mile from the locality of capture of the February-taken
specimens, are distinctly darker dorsally and slightly darker ventrally
than the three _meridionalis_ trapped in February and March, but
resemble the latter three in shortness of tail and in having short,
"peppered" dorsal pelage. We lack specimens of _chiapensis_ in summer
pelage. According to Hooper (1952:122) the summer pelages of _R. f.
chiapensis_ and _R. f. helvolus_ are indistinguishable. Our
_meridionalis_ differ from five summer-taken specimens of _helvolus_ in
shorter, more "peppered," and distinctly darker dorsal pelage.

Six skulls of _meridionalis_ were matched with six skulls of
_chiapensis_ having approximately the same amount of wear on the teeth,
and the series were compared, pair by pair, in various cranial
characters. In five of the six pairs _meridionalis_ had a less inflated
braincase, and smaller postpalatal foramina, and in each of the six
pairs _meridionalis_ had a greater depression in the frontonasal region
and posteriorly more acute incisive foramina. Four external
measurements and nine cranial measurements were compared using the
series of _meridionalis_, the series of _chiapensis_ from Guatemala,
and Hooper's (1952:213) measurements of seven _chiapensis_ from central
Chiapas. The lesser average and maximum total length of skull in
_meridionalis_ than in either series of _chiapensis_ suggests that
_meridionalis_ has a smaller skull. Externally, the lesser total length
of _meridionalis_ is largely owing to its shorter tail; there is little
difference in length of head and body between _meridionalis_ and
_chiapensis_. The longest tail among our _meridionalis_ is shorter than
the shortest tail among the _chiapensis_ (disregarding two Guatemalan
specimens of _chiapensis_ that probably had injured tails). The
interorbital breadth of _meridionalis_ is on the average greater and
the depth of cranium is less than in _chiapensis_. There is some
overlap in the range of each of these two cranial measurements, but in
all _meridionalis_ the interorbital breadth exceeds 42 per cent of the
depth of cranium, and in all _chiapensis_ is less than 42 per cent. The
length of the incisive foramina in _meridionalis_, expressed as a
percentage of the total length of the skull, is usually greater than in
_chiapensis_.

One of our specimens (KU 71389) contained four embryos that m