Thorius, also known as minute salamanders, pigmy salamanders, or Mexican pigmy salamanders, is a genus of salamanders in the family Plethodontidae. They are endemic to Mexico and found in southern Veracruz and Puebla to Guerrero and Oaxaca.
Thorius is the most species-rich tropical salamander genus relative to its distribution area. It is not uncommon for two or even three species to occur in the same place. In such cases, species have diverged in terms of body size and dentition, apparently facilitating niche differentiation.
The members of this genus are characterized by a small body — some species are less than 2 cm (0.79 in) in snout–vent length (tail roughly doubles the total body length). Their extreme miniaturization is accompanied by determinate growth and skeletal reduction. Their skeleton also shows unique features, such as ossifications of many elements that remain cartilaginous in other salamanders. Consequently, they are easy to distinguish from other salamanders. In contrast, they tend to be similar in appearance, making it difficult to distinguish species. However, molecular genetic methods have greatly facilitated identification of new species.