In 1980, F.J.S. and G.Y. reported the isolation of bursatellin, a metabolite from the sea hare Bursatella leachii pleii, and proposed for it structure 1. Recently, the research group at Naples collected two Mediterranean sea hares, Bursatella leachii leachii and Bursatella leachii savignyana, and isolated from them a compound that exhibited ¹H NMR spectral data nearly identical with that reported for bursatellin except for one additional low-field singlet observed between -7.90 and 8.20 ppm, the precise position being solvent dependent. This led the Italian workers to suspect the identity of the two compounds but also to question the original structural assignment, an assessment in which the Oklahoma investigators concurred after review of their original spectra. In the original report, the molecular formula was assumed from high-resolution mass analysis of the highest observable ion; in retrospect, this highest mass peak must be assigned an M⁺ - 18 ion status. Similarly, highest mass ions of the derived diacetate 2 and manganese dioxide oxidation product 3 were interpreted, then seemingly plausibly but with hindsight incorrectly, as M⁺ - HCN and M⁺ ions. Operating with the incorrect molecular formula led the original workers to disregard a low-field singlet (8.08-8.20 ppm singlet) in 1-3 and also a very broad, medium-intensity infrared absorption from 1600 to 1700 cm⁻¹. With the aid of higher field ¹H NMR and ¹³C NMR spectra plus some synthetic work, a revised structure of bursatellin is now reported.