Surely no area in North America has been so eagerly scoured for bryophytes as the Douglas Lake region of northern Michigan, and no other area has been so important in training a continuing supply of young bryologists. The course in bryology which George E. Nichols offered at UMBS from 1920 until his death in 1937 attracted good students from all over the country. It has continued in popularity and importance under the tutelage of William C. Steere, Margaret Fulford, A. J. Sharp, Paul M. Patterson, and the present author. This catalogue of 226 species, 17 varieties, and two forms of mosses is designed for the use of students at the Biological Station. Based on several years of careful, though intermittent work, it is a fairly complete and accurate list of the mosses of Cheboygan, Emmet, Mackinac, and Presque Isle Counties. These counties, adjacent to the Straits of Mackinac, are the ones most easily and most often visited by students of the Biological Station.