The morphology of diatoms which consistently occur in circular to oval colonies on the skin of North Pacific Dall’s porpoise was examined. Two previously described cetacean diatoms Stauroneis aleutica Nemoto and Stauroneis olympica Hustedt have been transferred to two new genera, Epiphalaina and Tursiocola respectively. A new entity, a gomphonemoid diatom Tripterion kalamensis is also described. The diatom diversity was greatest on Bering Sea animals. Less diversity was observed on animals from northern Honshu and Hokkaido. The Monterey Bay specimens were devoid of the most common diatom taxa observed at the other two locations . The somewhat differing diatom floras from these locations merit additional investigation since they may indicate that porpoises from the three areas do not intermingle. Chlorophyll fluorescence was observed in all taxa and colonies from animals landed in Japan suggesting that these diatoms may be photosynthetic.