sis of Characters

The characters used in the systematic study of the frogs in this group
are those usually employed in anuran systematics. Of the various
measurements and proportions, the snout-vent length and the relative
size of the tympanum to the eye apparently are of more taxonomic
importance than the others (Table 1). In all of the species the
tympanum is at least partially covered by a heavy, dermal
supratympanic fold, and in some specimens of _H. pachyderma_ the
tympanum is completely obscured. In two species (_H. bistincta_ and
_H. charadricola_) the snout is square, whereas in the other species
it is round.

The fingers are long and slender in _H. crassa_, _pachyderma_, and
_robertsorum_ and somewhat shorter with more webbing in _H. bistincta_
and _charadricola_. 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.

TABLE 1.--COMPARISON OF CERTAIN MEASUREMENTS AND PROPORTIONS
IN THE SPECIES OF THE HYLA BISTINCTA GROUP. (DATA FROM ADULT
MALES; MEANS ARE GIVEN IN PARENTHESES BELOW THE RANGES.)

A: Snout-vent length
B: Tibia length / Snout-vent length
C: Head width / Snout-vent length
D: Tympanum / Eye

====================================================================
SPECIES | N | [A] | [B] | [C] | [D]
---------------+----+-----------+-----------+-----------+-----------
_H. bistincta_ | 38 | 43.0-53.8 | 0.47-0.52 | 0.32-0.37 | 0.35-0.48
| | (46.3) | (0.49) | (0.34) | (0.42)
| | | | |
_H. | 10 | 35.3-44.4 | 0.50-0.54 | 0.31-0.33 | 0.30-0.37
charadricola_ | | (40.4) | (0.52) | (0.32) | (0.34)
| | | | |
_H. | 26 | 39.9-47.9 | 0.48-0.51 | 0.30-0.36 | 0.36-0.47
robertsorum_ | | (43.1) | (0.49) | (0.32) | (0.41)
| | | | |
_H. pachyderma_| 1 | 39.9 | 0.53 | 0.32