PREEBATORY. NOTE. 
This memoir is the third 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, December 21, 1895. 
