For some years members of this laboratory have known of the abundance of certain species of earthworms located in the final settling tank of the sewage treatment plant operated for the twin cities of Champaign and Urbana, Illinois. The writer became interested in making a seasonal survey of these larger Oligochaeta. This study has been carried on in the Zoological Laboratory of the University of Illinois under the supervision of Professor H. J. Van Cleave, whose ready counsel and advice are gratefully acknowledged by the author.