s slender and weakly
developed.

_Natural History._--_Hyla elaeochroa_ inhabits humid lowland tropical
forests in lower Central America and breeds in temporary ponds.
Clasping pairs, gravid females, and calling males have been found
mostly in June, July, and August. William E. Duellman informed me that
he also found males calling in mid-February, late April, and May.
Duellman (1967) reported detailed observations of the social
organization in the mating call of _Hyla elaeochroa_. The choruses in
this species are initially organized, but when many individuals call,
the chorus loses organization. I observed this species breeding in a
temporary pond at Puerto Viejo, Heredia Province, Cost Rica, in late
June. Calling males and clasping pairs were extremely abundant within a
few hours after a heavy rain. Males were mostly found calling from low
emergent herbs in the pond and less commonly from bushes and trees to
heights of six meters above the water. Calling males were also observed
at Ricon de Osa, Puntarenas Province, Costa Rica, in late July. These
breeding individuals were found in a shallow pond at the edge of a wet
forest. Calling stations were less than two meters in height. John D.
Lynch informed me that after a heavy rain in early August, he found
several hundred individuals congregated in a small grassy pond less
than a foot deep, at Rincon de Osa. Males were calling from sites on
grass stems a few centimeters above the water.

The mating call of _Hyla elaeochroa_ consists of short notes, repeated
at intervals of about 0.40 second. Each note has a duration of 0.12 to
0.24 second. The fundamental frequency varies from 48 to 65 cycles per
second, and the notes have 40-50 pulses per second; the dominant
frequency is at about 2,900 cycles per second (Table 2, Pl. 4A).

The eggs are deposited in a mass in the water near floating vegetation.
William E. Duellman informed me that he observed hatchlings oriented
vertically with the tip of the mouth at the surface of the water. They
gradually sank to bottom, but swam back to surface again. No additional
information is available concerning early development. Tadpoles have
been found in shallow grassy ponds in clearings and in temporary
woodland ponds.

_Tadpoles._--Three hundred and thirty-one tadpoles in various stages of
development are available. Thirty-five tadpoles in stage 35 have a mean
body length of 8.1 mm. (8.0-9.0 mm.), tail length of 17.7 mm.
(15.0-19.5 mm.)