Hope this will help you out!
Lepidobatrachus laevis: round pupils, smooth skin. a V-shaped vertebral ridge
L. llanensis: vertical pupils, vertebral ridge inconspicuous, back color brown or red, toad-like skin, bright orange spots around forelegs and hind legs
L. asper: rhomboid (square-like, oblique) pupils, back color grey or brown
And of course, there is the Freddie Krueger frog which is a man-made hybrid of L. laevis and L. llanensis.
Sexually mature males possess a dark blue-black throat (Budgett 1899; Cei 1980)
Budgett, J. S. (1899). ''Notes on the batrachians of the Paraguayan chaco, with observations upon their breeding habits and development, especially with regard to Phyllomedusa hypochondrialis, Cope. Also a description of a new genus.'' The Quarterly Journal of Microscopical Science, 42(167), 305-333.
Cei, J. M. (1980). ''Amphibians of Argentina.'' Monitore Zoologica Italiano, New Series Monografia, Firenze, 2, 1-609.