The type skeleton of ‘Ogmodirus’ was collected in 1909 by C. Boyce from the upper Greenhorn Limestone Formation (Lower Turonian, Late Cretaceous) of Cloud County (near Aurora), Kansas (Storrs, 1999; Schumacher & Everhart, 2005). The specimen, KUVP 441, is a partial skeleton consisting of partial vertebral column (51 cervical vertebrae, 18 caudal vertebrae), limb, and girdle elements. Originally named and briefly described by Williston & Moodie (1913), this long-necked plesiosaurian was later described and figured in more detail by Williston & Moodie (1917). ‘Ogmodirus’ is based on juvenile skeleton and is regarded as invalid (Storrs, 1999). For example, Welles (1962) considered the taxon a nomen vanum and Storrs considered it a nomen dubium and referred it to “?Elasmosauridae indeterminate”, because “the taxon cannot be characterized on the basis of the relatively poort type materiai…” (p.6). The species name was invalidly emended by Moodie (1916) from ‘martini’ to ‘martinii’. This change was followed by Williston & Moodie (1917) but the original spelling (‘martini’) takes precedence (Schumacher & Everhart, 2005).
The species name ‘O. martini’ honours Mr H. T. Martin “in appreciation of his long, faithful and intelligent work in the Cretaceous deposits of Kansas” (Williston & Moodie, 1917, p. 62–63).
A second species of ‘Ogmodirus’, ‘O. ischiadicus’, was transferred to the genus by Willison & Moodie (1917). However, given the invalid status of Ogmodirus as a genus, and the non-diagnostic state of the type material of the species (KUVP 434), this referral is unjustified (Storrs, 1999). KUVP 434 was originally described as ‘Polycotylus ischiadicus‘, later ‘Elasmosaurus ischiadicus‘, then ‘Ogmodirus ischiadicus‘. Welles (1943) erected a genus based on this material (Thalassiosaurus ischiadicus), but eventually discarded the taxon entirely (Welles, 1962) because it is based on non-diagnostic material (Storrs, 1999).