The major phospholipid of the extremely halophilic coccus, S. morrhuae, was purified and compared with the major phospholipid of the extremely halophilic rod, Halobacterium cutirubrum. Analysis was by infrared and nuclear magnetic resonance spectroscopy, mass spectrometry, and thin-layer chromatography. The last two procedures established structural identity of the coccal lipid with that of the rod, which had been shown to be the I-phosphatidylglycerophosphate derivative (2) of 2,3-di-O-dihydrophytylglycerol (1).