This work reports numerous atomic levels of Ar observed between 43.38 and 60 eV above the ground state of Ar I. These levels, until now undetected, produce weak perturbations on the double ionization curve obtained by electron impact. The cross section near this Ar++ threshold varies very nearly as a quadratic function. Most of the reported levels of argon have the configuration 3s3p54l 4l′. Ionic states are also responsible for some of these structures.