PREFATORY NOTE. 



This memoir is the fifth of a series designed to illus- 

 trate the investigations and explorations of the Hopkins 

 Seaside Laboratory, an adjunct of the biological labora- 

 tories of the Leland Stanford Junior University. The 

 series is issued under the patronage of Timothy Hopkins, 

 Esq., of Menlo Park, California. The present paper is 

 published with the co-operation of the California Academy 

 of Sciences, appearing simultaneously in its present form 

 and as part of the Proceedings of the Academy. 



Charles H. Gilbert, 

 Oliver P. Jenkins, 



Editors. 



Date of publication, June 19, 1896. 



