Melvius is a genus of vidalamiin amiid ray-finned fish from the Late Cretaceous.K. M. Cantalice, A. M. Martinez-Melo, and V. A. Romero-Mayén. 2019. The paleoichthyofauna housed in the Colección Nacional de Paleontología of Universidad Nacional Autónoma de México. Zoosystematics and Evolution 95(2):429-452 The type species, Melvius thomasi, was described by Bryant in 1987 from Hell Creek Formation.L. J. Bryant. 1987. A new genus and species of Amiidae (Holostei; Osteichthyes) from the Late Cretaceous of North America, with comments on the phylogeny of the Amiidae. Journal of Vertebrate Paleontology 7(4):349-361 A second species Melvius chauliodous, was named and described by Hall and Wolberg in 1989 from Kirtland Formation,L. Grande and W. E. Bemis. 1998. A comprehensive phylogenetic study of amiid fishes (Amiidae) based on comparative skeletal anatomy. An empirical search for interconnected patterns of natural history. Society of Vertebrate Paleontology Memoir 4. Journal of Vertebrate Paleontology 18(1, suppl.):1-690 and it is now considered to be one of the index taxa of the Kirtlandian land-vertebrate age.
Description Both species of Melvius were very large. A vertebral remain of M. thomasi would have belonged to a fish with standard length (length between tip of snout and the base of the caudal fin) of , and there are some specimens that exceed the height of that vertebra. Total length of this species would be at least . However, M. thomasi was dwarfed by M. chauliodous, as a specimen of M. chauliodous with abdominal centra which is wide would indicate a standard length of over , and there is even larger abdominal centra which is wide.
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