PREFACE vii 



Chapman, and Professor R. W. Tower, of the American Museum 

 of Natural History ; and Dr. F. B. Sumner, of the College of the 

 City of New York. For suggestions in regard to some of the 

 more important drawings we extend our thanks to Professors 

 E. L. Mark, G. H. Parker, W. E. Castle, Dr. H. W. Rand, and 

 Dr. W. McM. Woodworth, of Harvard University ; to Professor 

 J. S. Kingsley, of Tufts College ; and to Professor C. W. Hargitt, 

 of Syracuse University. 



Certain little-known species have been identified for us in the 

 tunicates, leeches, holothurians, crustaceans, gasteropods, and 

 sponges, respectively, by the following : Professor W. E. Ritter, 

 of the University of California ; Professor J. Percy Moore, of 

 the University of Pennsylvania ; Professor H. L. Clark, of Olivet 

 College ; Dr. Walter Faxon, of the Museum of Comparative 

 Zoology, Cambridge, Mass. ; Dr. L. P. Gratacap, of the American 

 Museum of Natural History ; Professor H.V.Wilson, of the Uni- 

 versity of North Carolina ; and Mr. Edward Potts, of Philadelphia. 



To Mr. D. C. MacLaren, of the DeWitt Clinton High School, 

 we are very much indebted for transposing into equivalent Eng- 

 lish letters the roots of the Greek derivatives. 



THE AUTHORS 



