Martinichthys is an obscure genus of Upper Cretaceous plethodid fish that was first described by C. E. McClung (1926). Less than 60 specimens of Martinichthys have been collected and most consist of only an elongated, bony rostrum which generally exhibits evidence of abrasion on the distal end. To date, only two complete skulls of Martinichthys have been collected and cervical vertebra are the only other bony elements associated with these skulls. Most of the skeleton apparently was cartilaginous or did not fossilize for other reasons. Field work by the authors (1993) between 1988 and 1993 has shown that the genus occurs only in the lower one third of the Smoky Hill Member, Niobrara Chalk of Western Kansas. All specimens for which locality data is available were found within a 6 meter interval between Hattin's (1982) stratigraphic Marker Units 3 and 5. This interval also corresponds to the upper part of Stewart's (1990) biostratigraphic Zone of Protosphyraena perniciosa and is of Late Coniacian age. In 1993, a Martinichthys rostrum was discovered that exhibited definite evidence of predator attack. The teeth of the fish, Pachyrhizodus caninus, or a small mosasaur would have left conical indentations similar to those that are visible on the dorsal and ventral sides of the rostrum. Damage which is attributable to a crushing lateral bite was also apparent on the specimen. This is the first evidence of predation on this genus.