PREFACE. vii 



Cambridge. The collection of scientific periodicals of the Smithsonian Institution is nn- 

 qnestionably the largest on this continent, and but for the wise policy of Prof. Henry, the 

 enlightened head of that establishment, the naturalists of America could not at this time 

 make any investigations involving historical researches. Next to the Smithsonian Institution 

 I have to mention the Academy of Natural Sciences in Philadelphia, the library of which 

 has accjuired the highest importance for naturalists, through the liberality with which Dr. 

 Wilson has supplied its wants. 



The Museum of Comparative Zoology in Cambridge contains specimens of all the 

 Acalephs described in this work which could be preserved. And I would take this oppor- 

 tunity to say, that, with proper care, a much larger number of these animals may be 

 preserved in a state fit for study than is generally supposed. Valuable specimens were 

 sent to me by Professor J. Leidy, collected by him in Long Island Sound and along the 

 shores of the Middle States, some of which he has himself described in his contributions 

 to the Marine Faunas of Rhode Island and New Jersey. Others, from the same locafities, 

 were presented to me by Mr. Samuel Powel of Philadelphia, among which I would 

 especially mention the Cordylophora described by Prof. Leidy. To my friend Theodore 

 Lyman I am indebted for fine specimens of several Hydroids of the Bay of Boston, and 

 to Mr. William Stimpson for others from the eastern shores of the Northern States. To 

 my friend T. G. Cary, and to my son Alexander Agassiz, who have enriched the Museum 

 of Cambridge with immense collections from California, I owe many specimens of Acalephs 

 from the west coast of North America. Captain W. H. A. Putnam, of Salem, to whom 

 our Museum is indebted for the most valuable collections from the Indian and Pacific 

 Oceans, has brought me a number of Medusa^ and Hydroids from the East Indies and 

 from the Gulf Stream, which, after years, are still in a good state of preservation. To 

 Mr. John McCrady I am indebted for an early communication of his contributions to the 

 history of the Acalephs of South Carolina. I would add also, that in the Aquarial 

 Gardens of Boston I have frequently had opportunities of observing many of our Hydroids 

 and Medusa? in a fine state of preservation. 



It is but proper, that, in leaving this volume to speak for itself, I should also mention 



the facilities constantly afforded me by the publishers for making it as worthy as possible 



of the extensive patronage it has received. 



LOUIS AGASSIZ. 

 Cambridge, October 31, 1860. 



