The Dover sole, Microstomus pacificus (Lockington) is a fairly large flatfish belonging to the family Pleuronectidae. It is not a true sole, but a flounder. However, through continued common usage of the term "sole" for most of the flounders along the Pacific Coast, this appellation has become recognized by the fishing industry and the different government agencies concerned. It has been known along the Pacific Coast under several different common names, such as slippery sole (California and Puget Sound), lemon sole (Vancouver), smear dab (Puget Sound), rubber sole and short finned sole (San Francisco), slime sole (California and Puget Sound), tongue sole, and Dover sole (Pacific Coast). The common name of Dover sole was first suggested by Mr. Stewart, employee of the New England Fish Co., Astoria, Oregon, around 1939 according to the Eureka fishermen. He probably associated Microstomus pacificus, the only representative of its genus along the eastern Pacific Coast, with Microstomus kitt Walbaum, which ranges from the White Sea into English waters and is probably taken off the Dover coast. The two species are very similar in general appearance and might well appear identical to an untrained observer, but in meristic counts and morphometric measurements they differ significantly. In 1946, Clemens and Wilby used the name Dover sole in their Fishes of the Pacific Coast of Canada, and in 1948 it was adopted as the official name in California by the Department of Fish and Game. It is evident that the name Dover sole has a greater marketing value than some of the other names, such as slime sole, slippery sole, etc., with their rather unappetizing connotations. Although the range of the Dover sole extends from Southern California to Alaska, it is important commercially only from San Francisco northward along the Oregon coast. Small amounts have been landed in Washington and British Columbia, but the centers of fishing are at Fort Bragg and Eureka in California, and at Newport and Astoria in Oregon. South of Monterey it is not found in great abundance. In developing a management program for the conservation of a fisheries resource, a knowledge of the biology of the species concerned is important. Full utilization of the population is desirable, but a balance must be maintained between the recruitment and the total mortality. Regulation of fishing areas, closed seasons, restrictions on destructive gear, and limitations on total catch are tools that may be used in the maintenance of a fisheries resource at the most productive level, but their use should be based on sound reasoning and biological facts. It is in the hope of providing a few of the required facts that this study is presented. In the course of this investigation approximately 3,200 specimens of Dover sole were examined during the period from July, 1948, to October, 1949. The bulk of the material was gathered from commercial fishermen and dealers in the Eureka region, although a small amount of sampling was conducted at Fort Bragg. After the fish are taken from the vessel during normal commercial handling, they are weighed by the dealer and dumped in a pile near the end of a conveyor system. The measuring board was placed on a fish box or bench as close to this source of supply as possible, and specimens were taken at random from the pile. Each fish was weighed, laid on the board with the nose against the end plate and the total length measured. The abdominal wall was cut to determine the sex and to obtain gonad samples. Stomach contents were sampled in some cases. If scales were required they were taken by means of a pair of forceps and either placed in an envelope or put directly on a slide. Otoliths were taken by holding the fish firmly with the left hand (thumb in the lower eye orbit) and making a diagonal cut into the head exposing the brain and inner ears. Otoliths were taken from both sides, placed in an envelope, and preserved dry. All data were recorded on a white plastic sheet with a lead pencil. In this way, the sampler, with wet slimy hands, could write down the necessary information and by washing the sheet in water have a clean neat record. After transferring the information to paper, the plastic sheet was washed with a cleanser to remove the pencil marks.