In 1941, Fernholz and Ruigh (1) convincingly demonstrated that campesterol and campestanol differ from 22,23-dihydrobrassicasterol and ergostanol solely in the optical configuration at C-24. Since then it has been shown that this C-24 epimerism is not infrequently encountered among naturally occurring sterols, and that the C2s-sterols from marine invertebrates such as the stellasterols and stellastenols (2), neospongosterol (3) and chalinasterol (4) predominantly belong to the campestanol series. In conformity with the customary designation of steroid epimers, it is here proposed to refer to the ergostanol and campestanol series as the 24-(a)-and 24-(0)-methylcholestanol series, and following a suggestion by Ruigh (5), to write the 24-methyl group above the side chain in the «-series (I) and below the side chain in the 0-series (II).

In 1904, Henze (1) isolated from the Mediterranean sponge, Suberites domuncula, a new sterol which he named spongosterol. The unusual properties of this sterol left no doubt about its difference from cholesterol which until then had been regarded as the typical sterol of all animals. A few years later (2), the same author presented evidence which indicated spongosterol, m.p. 123-124°, [a]D -19.6°, to be a saturated sterol of the formula C27H48O, and therefore an isomer of cholestanol and coprosterol. Notwithstanding its saturated character, spongosteryl acetate reacted readily with bromine in glacial acetic acid to form a monobromide, Cgg^gBrOg, m.p. 156°, which Henze regarded as a substitution product. Since then several other new sterols have been isolated from animals, particularly marine invertebrates, but as far as the authors are aware, no further information on spongosterol has been published.In connection with a systematic study of the sterols of sponges, now in progress in this laboratory, it appeared of particular interest to reinvestigate this unusual sterol. Modem knowledge of the optical properties of steroids makes appear quite unlikely the natural occurence of a levo-rotatory, saturated sterol. It seemed equally improbable that a saturated steryl acetate reacts readily with bromine to form a monobromide under the mild conditions used by Henze. Present circumstances made it impossible to obtain the Mediterranean sponge as source material for the isolation of spongosterol. A very close relative of this species, however, Suberites compacta, is quite common in certain regions of the coastal waters of New England. The dried sponge contains about 0.7% of a sterol the properties of which show such great similarity with those reported for spongosterol as to leave little doubt about the identity of the two sterols.

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Chalina arbuscula Verrill is one of the more common sponges of the coastal waters of New England. In its dried state it contains on the average about three per cent of acetone-soluble material, one to one and one-half per cent of unsaponifiable matter and from one-half to six-tenths of one per cent of a sterol of a degree of uniformity rarely encountered in sponges. The properties of 1450; [