Hydroids of the Pacific Coast of Canada and the United States is an attempt to give a brief description, with figures, of every hydroid species known to occur along the Pacific Coast of Canada and the United States, together with its distribution within this area. It is intended to provide the Pacific zoologist with a reference, easily understood, to every species of hydroid reported from the coast. Keys to families, genera, and species have been included to facilitate diagnosis. Much of the information presented has already been published, but in widely scattered papers, some of them long out of print. The new contribution is largely in the extensive addition to the distribution records, for which many thousands of specimens have been examined.

Each plate accompanied by guard sheet with descriptive letterpress.