2 AMERICAN HYDROIDS. 



The material in the U. S. National Museum relating to the Ilydroida had never been worked 

 over when the present writer consented, at the request of the late Doctor Goode, Assistant Secre- 

 tary of the Smithsonian Institution, to prepare a monographic account of the whole group. The 

 author was persuaded that the time had come for a gathering together of our knowledge 

 regarding the Hydroida, a review of the work done by other authors, a working over of the vast 

 accumulations resulting from the various Government expeditions and the "Bahama expedition" 

 from the University of Iowa, and a presentation of the whole subject in monographic form. 



It was deemed best to publish the work in several sections for convenience in handling and a- 

 more prompt appearance of the results of study in certain groups, and the Plnmulurida- was 

 selected as the first group for discussion, because the amount of new material was probably 

 greater than in other families, and for the further reason that it would take a greater amount of 

 time to prepare any acceptable account of groups involving the investigation of the hyclroid 

 medus;e, perhaps the most intricate and perplexing class of forms embraced in the order Hydroida. 

 It was hoped, moreover, that Dr. Alexander Agassiz would, in the mean time, complete his 

 promised work on the Acalephse, including the accession of knowledge which has been accumu- 

 lating since the appearance of his ''North American Acalephic" in 18(55. In this case it would be 

 unnecessary to investigate the hydroid medusa; to any considerable extent in connection with this 

 monograph. 



Whatever of merit appears in the following pages is very largely due to the naturalists who 

 have almost without exception responded to my great need for their generous aid. To mention all 

 who have given assistance would involve the naming of nearly every living naturalist who has 

 made a special study of the Hydroida. 1 can not, however, omit acknowledgment of the help 

 rendered by the following: My thanks are especially due to Dr. Alexander Agassi/,, who obtained 

 for me the privilege of occupying the Harvard table at Naples; to Prof. A. B. Verrill, for much 

 valuable material from the Yale Museum, and even more valuable advice; to Hon. J. J. Brice, 

 former U. S. Commissioner of Fish and Fisheries, for placing at my disposal the facilities of the 

 laboratory at Woods Hole, Massachusetts; to the late Sir William H. Flower, for permission 

 to examine the Challenger Plumularida* in the British Museum (Natural History); to the Eev. 

 Canon A. M. Norman, for specimens and advice; to the veteran naturalist, the late Prof. G. J. 

 Allman, for helpful suggestions; to the officers of the Marine Biological Association of the 

 United Kingdom, and especially E. I. Allen, esq., for laboratory facilities at Plymouth; to Prof. 

 Anton Dohrn, Prof. Paul Meyer, Prof. Hugo Eisig, and Dr. Salvatore Lo Bianco, of the Zoological 

 Station in Naples; to Prof. William M. Bale, for specimens of Australian Plumularid.e and 

 much excellent advice; to Prof. W. Baldwin Spencer, for literature and specimens; to Dr. Gottlieb 

 Marktanuer-Turueretscher, for his papers on the Ilydroida; to Prof. Eobert von Lendenfeld, 

 for literature and correspondence, and to Dr. Walter Faxon, lor facilities in examining the types 

 in the Museum of Comparative Zoology. 



