. It is probable that _muticus_
and _calvatus_ would be capable of interbreeding if they were not
spatially isolated. It should be pointed out, however, that there is no
evidence of intergradation between _muticus_ and _calvatus_ in the
lower Mississippi Valley as has been reported for the subspecies of _T.
spinifer_ (Conant and Goin, 1948), and that the degree of difference
between _calvatus_ and _muticus_ is greater than that between some
subspecies of _T. spinifer_.

_Specimens examined._--All the localities listed below are
plotted on the distribution map (Fig. 1). Only those
specimens of _T. muticus muticus_ are listed that serve to
delimit the range of _T. m. calvatus_. Fortunately, the
identification of the specimens of _muticus_ is certain as
all show the characteristic juvenile pattern, except the
large female, TU 7543, from southeastern Louisiana. USNM
95133-34 (carapaces and plastrons only) and TU 17236 are
females, which lack the diagnostic spotted pattern of
_calvatus_; the former are referred to this subspecies on
geographic grounds (Pearl River at Columbia, Mississippi).
TU 17236, from the Amite River, is dubiously relegated to
_calvatus_ on the supposition that this river and others in
the Lake Ponchartrain drainage will yield the characteristic
juveniles.

_Trionyx m. calvatus_ (33 specimens): TU 13473, 16682,
17301, 17302-.1, KU 47116 (skull only), Escambia River, 2
miles east, 1 mile north Century, Escambia Co., Florida; TU
17303-.4, 17304-.3, Pearl River, Varnado, Washington Par.,
Louisiana; TU 17306-.3, Pearl River, 9 miles south
Monticello, Lawrence Co., Mississippi; TU 16956, KU
47117-19, USNM 7655, Pearl River, vicinity of Monticello,
Lawrence Co., Mississippi; TU 17236?, Amite River, near
Baton Rouge, Louisiana; TU 13795, Bogue Chitto River, Enon,
Washington Par., Louisiana; TU 17305, no data, Louisiana;
USNM 95133-34, Pearl River, Columbia, Marion Co.,
Mississippi; UI 31071, Pearl River, 14 miles northeast
Jackson, Rankin Co., Mississippi; Uncatalogued, see page
523, Leaf River, 3 miles southeast New Augusta, Perry Co.,
Mississippi.

_Trionyx m. muticus_ (6 specimens): TU 5989, Ouachita River,
Monroe, Ouachita Par., Louisiana; TU 7543, Vacherie, St.
James Par., Louisiana; CNHM 7845, Gayles, Caddo Par.,
Louisiana; USNM 92