1. Morphological and cytological observations of a microhalophilic alga are described and illustrated. 2. Clonal cultures isolated from a barrel of water at the Marine Biological Laboratory, Woods Hole, Massachusetts, proved to be members of an undescribed species of Chlamydomonas. 3. The organism is described as C. microhalophila sp. nov., a member of the Chlamydella section of the genus. 4. The organism tolerates concentrations of salts (predominantly NaCl) up to approximately 1.0%, and responds by marked increase in growth in concentrations up to approximately 0.5%. 5. Its homothallic sexual reproduction and zygote germination are described and figured. 6. Its chromosome number has been determined as n = 16 ± 1. 7. Cultures of the organism have been deposited in the Culture Collection of Algae, Department of Botany, Indiana University, and herbarium specimens have been sent to the Chicago Natural History Museum.