This dissertation reports the results of an investigation of the bottom fauna under the deeper water of Cayuga Lake. It supplements a broad limnological study of the lake that has been in progress by the limnological laboratory of the New York State College of Agriculture since the summer of 1950. The present paper presents a qualitative and quantitative inventory of the profundal benthic fauna. It has been designed to observe the seasonal changes that the components of the fauna under, and to obtain some information of the life historories of some of the species that live in this community.