INTRODUCTION. 177 



applied by some modern authors to one species, by others to another, especially 

 when, as is often the case, the original figures do not agree very well with any 

 actual form? If we abandon them altogether, they remain as constant sources 

 of confusion, for they cannot be considered nomena nuda. If used there is 

 the danger of applying them to wrong species, their true identity being discovered 

 later. More than one such case has occurred. In the present Memoir I have 

 used an old name whenever the figures allow. Otherwise they are given in 

 the doubtful list (p. 354-357). Many nomena nuda have been used, espe- 

 cially by the older writers; these are omitted. 



The classification employed is based on that outlined by Chun ('97b), 

 because of the various schemes which have been proposed, this most nearly 

 represents the natural relationships of the several groups. But I have not 

 hesitated to make various changes which more recent studies have shown to 

 be necessary. The family relationships of the Calycophorae form such a case, 

 to which attention is called. 



It is a pleasure to acknowledge my indebtedness to Alexander Agassiz, the 

 lamented leader of the Expedition, not only for the opportunity to accompany 

 him on the Cruise, but for encouragement without which the present Memoir 

 could never have been prepared. 



