William Edward Duellman, A Review of the Frogs of the Hyla bistincta Group
“ Breeding males of Hyla pachyderma have moderately large nuptial spines; the other species have small spines, except H. charadricola in which spines apparently are absent. A well-defined thoracic fold is present in H. pachyderma, and a weak fold is present in H. robertsorum; the other species lack folds. In all species there is an anal sheath; this sheath is longest in H. bistincta, in which the anal opening is directed ventrally at the level of the lower edge of the thighs. ”
