The fingers are long and slender in H. crassa, pachyderma, and robertsorum and somewhat shorter with more webbing in H. bistincta and charadricola.
"A Review of the Frogs of the Hyla bistincta Group"
William E. Duellman
A well-defined thoracic fold is present in H. pachyderma, and a weak fold is present in H. robertsorum; the other species lack folds.
"A Review of the Frogs of the Hyla bistincta Group"
William E. Duellman
Both H. pachyderma and H. crassa seem to be advanced beyond H. robertsorum.
"A Review of the Frogs of the Hyla bistincta Group"
William E. Duellman