IV PREFACE. 



iirally turned to the Museum of Comparative Zoology at Cambridge 

 as our richest depository of Natural History, and was not disap- 

 pointed in finding a valuable collection of New England Shells. 

 Professor Agassiz kindly put these at my disposal, and Mr. J. G. 

 Anthony spared no pains to assist me in selecting specimens for 

 figuring. The Museum of the Peabody Academy at Salem also fur- 

 nished a large numljer of specimens, which were drawn on wood by 

 Mr. E. S. Morse with his usual accuracy. I am indebted also to 

 Mr. Morse for the identification of most of the smaller and more 

 difficult species, and to him, indeed, belongs almost the entire 

 credit of the illustrations in the text. 



I was unable to carry out Dr. Gould's plan of reprinting the 

 original copperplates, as they were not to lie found. I thought it 

 best to have new figures drawn on wood rather than reproduce the 

 •old ones. This fact will account for the frequent discrepancies be- 

 tween the descriptions and figures, especially as regards measure- 

 ments, as the specimens selected by me for figuring are often larger 

 and finer than those from which Dr. Gould drew his descriptions. 



Most of these woodcuts were engraved by Mr. Henry Marsh, so 

 well known for his beautiful illustrations of" Harris's Insects." 



Dr. Gould had prepared for engraving many beautiful drawings 

 of Nudibranchiata. Professor Agassiz has added largely to these, 

 and also has furnished many drawings of Tunicata and Cephalo- 

 poda. These I have grouped into plates which have been printed 

 by chromo-lithography, by Messrs. Bowen & Co., of Philadelphia, in 

 a most creditable manner. 



I have retained the references to the figures of the original plates 

 and have continued from them the numbering of the figures in tlie 

 new edition, first in the plates, and then in the text. The number- 

 ing of the plates in this edition commences with XVI., thus allow- 

 ing for the fifteen original copperplates, although they were not 

 numbered. 



In addition to the gentlemen named above, and in various notes 

 throughout the text, I am indebted to Dr. W. Stimpson and Dr. P. 

 P. Carpenter for valuable assistance in preparing the work. 



On account of the incompleteness of Dr. Gould's manuscript, and 



