This small hylid is abundant in the Tepalcatepec Valley to elevations of about 1000 meters; it was found infrequently on the coastal lowlands. Males call from bushes in and around flooded fields and ditches, from grasses and small herbs in the water and from vegetation overhanging small streams. The call consists of a series of short, high notes, somewhat reminiscent of a katydid's song. In the dry season occasional males were heard calling from irrigated fields near Apatzingán. In the daytime individuals were found in the axils of leaves of the elephant-ear plants (_Xanthosoma_). In living individuals the dorsal color usually is uniform pale yellow; often the lateral white stripe is barely visible. The vocal sac is bright yellow, and the iris is pale gold. In some individuals there are scattered dark brown spots or flecks on the back and upper surfaces of limbs. Twenty males from Apatzingán have the following measurements: snout-vent length, 22.8-26.0 (25.0) mm., tibia length, 10.7-13.6 (12.6) mm.; head width, 7.2-8.0 (7.6) mm., head length, 7.1-8.1 (7.7) mm. ~Hypopachus caprimimus~ Taylor _Hypopachus caprimimus_ Taylor, Univ. Kansas Sci. Bull., 26:526, November 27, 1940.--Agua del Obispo, Guerrero, México. Buena Vista; Copuyo (6); Charapendo (3); Cofradía; Jaramillo; Jungapeo; San Salvador; Tuxpan. Specimens of _Hypopachus_ from the Balsas drainage in Michoacán have characters consistent with topotypic _H. caprimimus_. Eleven specimens from the southern edge of the Mexican Plateau all have the flanks darker than the dorsum, a distinct and continuous dark stripe from the occiput to the groin, a large dark spot in the inguinal region, and a pair of dark transverse stripes on the thigh and shank (Pl. 6, Fig. 1). With the exception of three specimens from Charapendo, all have a predominantly brown venter with round, cream-colored spots. Peters (1954:8) referred specimens from Buena Vista and San Salvador to _Hypopachus oxyrrhinus_. He stated that the specimen (BMNH 1914.1.28.150) from San Salvador had flanks much darker than the dorsum and a well-defined continuous stripe from the occiput to the groin; this specimen has the characters of _H. caprimimus_. The specimen (BMNH 1914.1.28.151) from Buena Vista resembles _H. oxyrrhinus_ in some characters, but it is not like _H. oxyrrhinus ovis_ on the Mexican Plateau in Michoacán. The specimen has paired transverse stripes on the hind limbs as does _H. caprimimus_, and is here referred to that species. In Michoacán this species has been collected in arid tropical scrub forest at elevations of 200 to 1800 meters in the northern foothills of the Sierra de Coalcomán, the Tepalcatepec and Tuxpan valleys, and on the lower slopes of the Cordillera Volcánica. Calling males have been found along streams. One specimen from Charapendo was regurgitated by a _Leptodeira maculata_. ~Hypopachus oxyrrhinus ovis~ Taylor