The number of transverse bars on each thigh and shank varies from five to eight. The white stripe above the anus and the stripe from the snout along the side of the head are invariably present. In some of the largest individuals the brown reticulations on the anterior surface of the thigh extend onto the ventral surface; in these specimens brown flecks are present on the ventral surfaces on the shanks.
The tympanum is proportionately larger in females than in males; the variation in size and proportions is given in Table 2. The total number of prevomerine teeth varies from 13 to 18 (mean, 15) in five adult males and from 10 to 12 (mean 11) in two females.
The testes in all adult males are granular, ovoid in shape, and greatly enlarged. The lengths of the left testis in each of the five males are 11.0 to 23.5 (mean 14.6) mm.
Comparisons.—On the basis of external appearance and certain cranial characters (large frontoparietal fontanelle, broad sphenethmoid, large nasals broadly separated medially having thin lateral processes articulating with the palatines, short squamosal not articulating with the maxillary, and quadratojugal present and articulating with the maxillary), Hyla altipotens can be associated with the Hyla taeniopus group (Duellman, 1965, Lynch and Smith, 1966). Hyla altipotens can be distinguished from all of the other members of the group by its narrow head, pointed snout in both sexes, and uniformly yellow throat and belly.
Small brown individuals of Hyla altipotens superficially resemble adult Hyla pinorum. The latter species has a covered tympanum, less webbing on the hands, and a short, blunt snout.
Remarks.—This stream-breeding frog is like Hyla taeniopus in having greatly enlarged testes, which possibly through the production of vast quantities of sperm are an adaptation for successful breeding in torrential streams (Duellman, 1965:164).
All individuals were found in trees and bushes near streams in cloud forest at night in February. The type locality is the same as that of Hyla pentheter and Hyla thorectes, discovered by Kraig Adler in June, 1964. Our field work there in February, 1966, resulted in finding Hyla altipotens, H. pellita, and Ptychohyla leonhardschultzei, but no individuals of the species found by Adler. A visit to the same locality in August, 1966, revealed no individuals of either H. altipotens or pellita; instead pentheter and thorectes were found along the stream.
Duellman (1965:166) listed a specimen (TCWC 16184) of Hyla chaneque from Los Fustes, 3 kilometers east of San Sebastian, Oaxaca. Rëexamination of this specimen reveals that it is Hyla altipotens. The frog was obtained by Dilford Carter on April 29, 1960; it was under a rock at the edge of a stream in an oak-pine-cypress association at an elevation of 1800 meters.
The specific name altipotens is Latin, meaning mighty, here used in allusion to the supposed potentiality of fertilization by the production of vast quantities of sperm in the large testes.
Plectrohyla hartwegi new species