Fig. 2. Adult male of Hypopachus oxyrrhinus ovis from Tangamandapio, Michoacán. × 3.
4. A distinct, pale-colored, diagonal lateral stripe is found in females only from localities outside of the Balsas-Tepalcatepec Basin; females from the basin have a spotted dorsum.
5. Males from the Balsas-Tepalcatepec Basin usually have a broad middorsal line that is yellow or pale tan; those from outside the basin have either a narrow middorsal line or none.
6. Males from the Balsas-Tepalcatepec Basin have low, scattered dorsal tubercles (Fig. 3); males from outside the basin have a concentration of tubercles in a broad band on the back (Fig. 4).
Therefore the nature of the cranial crests is of little value in separating two populations, but the color pattern of the females and the nature of the dorsal tubercles of the males do show distinct differences. Furthermore, certain differences in size and proportion are evident; Bufo marmoreus is a slightly larger toad and has a relatively longer tibia and longer head than perplexus (Table 2).
Table 2.—Comparison of Certain Measurements and Proportions in Bufo marmoreus and B. perplexus. (Means Are Given in Parentheses Below the Ranges.)
| Tibia length | Head length | ||||
| Species | Sex | N | Snout-vent length | Snout-vent length | Snout-vent length |
| B. marmoreus | ♂ | 15 | 61.5-72.5 | 35.9-41.6 | 28.3-33.3 |
| (65.2) | (39.0) | (31.6) | |||
| B. perplexus | ♂ | 20 | 50.0-59.0 | 33.7-38.1 | 26.4-31.1 |
| (54.9) | (36.4) | (29.5) | |||
| B. marmoreus | ♀ | 7 | 68.0-76.0 | 33.0-36.8 | 26.8-32.6 |
| (70.7) | (34.7) | (29.6) | |||
| B. perplexus | ♀ | 6 | 64.1-69.8 | 32.4-36.9 | 25.1-29.0 |
| (66.8) | (35.5) | (27.5) |
Taylor (1943a:347) described Bufo perplexus from Mexcala on the Río Balsas in Guerrero. Among the many paratypes are specimens from Tonolá, Chiapas, and Tehuantepec, Oaxaca. These apparently were referred to perplexus solely on the nature of the cranial crests. All of the specimens examined during the course of the present study from the lowlands of Veracruz and from the Pacific lowlands from Sinaloa southward to Chiapas are referable to Bufo marmoreus; those from the Balsas-Tepalcatepec Basin are referable to Bufo perplexus, as defined above. Ten specimens from Chilpancingo, Guerrero (UMMZ 115352), do not readily fit either species. Perhaps there is gene exchange between the inland and coastal populations through the relatively low pass at Chilpancingo, at the mouth of the Río Balsas, and near the convergent headwaters of the Río Coahuayana and Río Tepalcatepec in southern Jalisco. If this can be demonstrated, then Bufo perplexus would have to be considered as a subspecies of Bufo marmoreus, instead of an allopatric species.
Bufo perplexus Taylor