To also add to what the other posters mentioned, the Great Plains Ratsnake(P. emoryi) has a divided anal plate, whereas the the Prairie kingsnake(L.c.calligaster has a single anal plate.
Also, the head shape in the calligaster is less distinct from the neck than in emoryi. The top of the head in emoryi generally has more of a spearpoint(chevron) pattern than does the Prairie king that generally has more of a mottled "filigree" pattern.
Additionally, the subcaudal scale counts(underside past vent) in both are as follows.....the counts in males being higher in both.
P.emoryi subcaudals..........58-83
L.c.calligaster subcaudals...38-57
~Doug
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"a snake in the grass is a GOOD thing" 
