The most distinctive external feature of Xantusiidae is the lack of eyelids. The eyes are covered by a large, transparent scale ("spectacle" or brille) similar to that in snakes and many geckos. The family often is erroneously said to be characterized by having vertically elliptical pupils, but this condition is present only in Xantusia. Cricosaura and Lepidophyma have round pupils. The belly is covered by a series of transverse rows of large, rectangular scales, and there are enlarged plates on the dorsal surface of the head. Body size differs tremendously among the species, from a maximum snout-vent length of only 1.5 in (3.7 cm) for the desert night lizard (Xantusia vigilis) to 5 in (12.7 cm) for the yellow-spotted night lizard (Lepidophyma flavimaculatum).
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