Occasional Papers of the Museum of Zoology 5 



spawning season in the spring, and he took this to mean that 

 it required four years for the whole life cycle. The three 

 groups were arranged by him as follows : larvae of the third 

 year, 17 to 20 centimeters; those of the second year, 9 to 11 

 centimeters, and those of the first year, 3 to 6 centimeters. 



In the same form and from the same locality, the writer 

 (1921) found larvae of five different sizes during the month 

 of August, indicating a life cycle of at least five years. This 

 conclusion was based on measurements of 167 larvae. Sim- 

 ilar results were obtained from collections made in February 

 and during the months of April, May, and June. 



Nature of Material. — In 192 1 two collections of another 

 species of brook lamprey, Ichthyomyson unicolor (see Creaser 

 and Hubbs, 1922), were obtained by Messrs. Carl L. Hubbs 

 and Charles W. Creaser, one on August 25 in Thunder Bay 

 River southeast of Atlanta, Michigan, consisting of 229 speci- 

 mens, and another on August 26 in Gilchrist Creek, a tributary 

 to Thunder Bay River, of 134 specimens. In the former col- 

 lection there were two metamorphosing individuals and in the 

 latter another one. These collections were kindly turned over 

 to the writer for a determination of the rate of growth and 

 of the length of the life cycle. 



Ichthyomyson fossor, a synonym of this species, was 

 described by Professor Jacob E. Reighard and Mr. Harold 

 Cummins in 191 6 from specimens obtained in Mill Creek, 

 near Dexter, Michigan. The adults which formed the basis 

 for the description ranged in size from 112 to 149 millimeters 

 and the larvae from 80 to 158 millimeters. The time of meta- 

 morphosis and the duration of the larval period were not 

 determined. 



Length of the Life Cycle. — ^The specimens of both collec- 

 tions were carefully measured and the measurements were 



