Mexican beaded lizard generic name "Heloderma" means "studded skin", from the Ancient Greek words "hêlos" (ἧλος)—the head of a nail or stud—and "dérma" (δέρμα), meaning skin. Its specific name, "horrĭdum", is the Latin word meaning rough or rude. The four subspecies of beaded lizard, elevated to full species in 2013, are: Adult beaded lizards range from in length. They are substantially larger than the Gila monster, which only reaches lengths of . The snout-to-vent length of a beaded lizard averages . The average body mass of an adult beaded lizard is , about 45% heavier than the average mass of a gila monster,
Southern alligator lizard the fact that the back and belly scales of these lizards are reinforced by bone, as they are in alligators. Three subspecies can be distinguished: the California alligator lizard ("E. m. multicarinata"), the San Diego alligator lizard ("E. m. webbii"), and the Oregon alligator lizard ("E. m. scincicauda"). The subspecific name "webbii" is in honor of Thomas Hopkins Webb (1801–1866) who was Secretary of the United States and Mexican Boundary Survey (1848–1855). The subspecific name "scincicauda" means "skink tail". The southern alligator lizard measures from 3 to 7 inches (7.3 - 17.8 cm) in snout-to-vent length (SVL). Including tail, it