Ventral view. Scale is in mm. Quoting from
Key to Florida Ground Beetles key of genus
Calosoma vs.
Carabus: Metepimeron longer than wide.--->
Calosoma
A definition of epimeron is "the part of the side of a somite external to the basal joint of each appendage". I'm not sure about this character, but hope to understand it in the future.
Compare ventral view of
Carabus vinctus: