This minute alga was first found in i897 growing in a culture with other small algae in the botanical laboratory at the University of Basel, Switzerland. Though the exact source of the culture cannot be stated, it is known to have come from the vicinity of Basel. The alga was next found in a culture taken from some epiphytic mosses and liverworts from Guatemala presented to the writer by Miss F. G. SMITH in January I909.Though search has often been made for it in different parts of the United States, it has never been observed, and any record of its occurrence in the country has escaped notice by the writer. In its early vegetative state the alga shows nothing distinctive and might easily be taken for a small Chlorelia or the germinating zoospore of some higher form (fig. I), but in the shape of the adult cell and in its mode of reproduction it stands unique among all green algae. In shape the mature cell is pyriform, either perfectly symmetrical or somewhat irregular, 0.0084-0.0II2 mm. in length and o.oo56-o.007 mm. at its greatest breadth (figs. 2, 3). The color is a very light green. The parietal chloroplast is cup-shaped, with the large opening either at one side or at the smaller end of the cell, so that a portion of the cell is always colorless. A large vacuole is present (fig. 5a). No starch was found in either the material from Switzerland or in that from Guatemala. In the former no reaction for cellulose was obtained with the chloriodide of zinc, but in the latter a distinct reaction was shown with that reagent. A further difference between the two forms was noted in the number of nuclei. In the Swiss material the mature cells when stained with hematoxylin showed four distinct nuclei, and in some instances eight were counted; while in the material from Guatemala a cell Botanical Gazette, vol. si] [360