Stenomylus tubutamensis was reported as the smallest species of the genus by Ferrusquia-Villafranca (1990). Eight diagnostic characters, or groups of characters were listed as autapomorphies for S. tubutamensis. Three additional characters were shared with other species of Stenomylus. A re-analysis of S. tubutamensis was made by comparing its diagnostic characters to the same characters based on larger samples of other species of Stenomylus. The re-analysis shows that S. tubutamensis possesses one autapomorphy based on the original diagnostic characters. Nor does the S. tubutamensis possess a unique combination of characters. The study shows that many characters, especially raw dental metric characters, of the Stenomylinae are quite variable in their expression and can only be assessed by examination of means and ranges of variation based on large samples. The diagnosis of S. tubutamensis is revised. Relative to the other species of Stenomylus, S. tubutamensis is now diagnosed by the possession of the smallest upper canine, smallest P1, shortest average p1–p2 diastema, shortest average C–P1 diastema, shortest average p2–p3 diastema, and narrow, slit-like fossettids on the lower molars. The abandonment of the subgenera Stenomylus and Pegomylus is proposed.