10 THE APODOTJS HOLOTHUBIANS 



volved a number of changes which, however unwelcome, were bound to be 

 made sooner or later. The author lays no claim to infallibility, however, and 

 does not expect that no errors will be found in his results. Lack of knowl- 

 edge or poor judgment on his part, coupled with the inadequate descriptions of 

 early writers, afford many loopholes for mistakes. 



In conclusion, I desire to express the great obligation I am under to Mr. 

 Richard Eathbun, the Assistant Secretary of the Smithsonian Institution, for 

 his unfailing courtesy and many helpful suggestions, and to Miss Mary J. 

 Eathbun, for much kind assistance in connection with nomenclature and illus- 

 trations. My friend, Professor L. T. Larsen, of Olivet College, has afforded me 

 invaluable assistance in my effort to have philologically correct the new names 

 I have been obliged to coin. I am also greatly indebted to Dr. Hjalmar 

 Ostergren, of Upsala, who by his letters and kindness in sending me specimens, 

 as well as by his publications on the Synaptidae, has proved an invaluable aid. 



Finally, Dr. W. K. Fisher has very kindly permitted me to have advance 

 sheets of his valuable memoir on Hawaiian Holothurians, and these have 

 enabled me to include his work herein. 



CAMBRIDGE, MASS., April 1, 1907. 



