PREFACE. 
lu this memoir we have endeavored to give concise descriptions of 
all the species of fishes known to inhabit the waters of Korth America, 
north of the boundary between the United States and IMexico. 
The classification which we have adox)ted is essentially based on the 
views of Professors Gill and Cope, who have, it seems to us, been more 
fortunate in reflecting nature in their groupings of the fishes than have 
any of the European systematists. In our arrangement of the families 
and genera, we have endeavored to avoid, on the one hand, unnatural 
associations, and on the other, subdivision beyond reasonable limits. 
Genera to which we have been unable to give precise definition have 
been rarely adopted. , 
The rules of nomenclature generally recognized by naturalists, and 
recently admirably formulated by Mr. W. H. Dali, have been followed 
without deviation, except such as may be due to ignorance of all the 
facts in any particular case. Most of the present confusion in nomen- 
clature is due to the neglect of established rules, and the only way out 
of this confusion is through the rigid enforcement of these rules. There 
is little hope for uniformity in nomenclature so long as individual prefer- 
ence or caprice is allowed to affect it. 
We are under obligations to Prof. Spencer P. Baird, to Prof. G. 
Brown Goode, and to Dr. Tarleton H. Beau, for many aids, especially 
in connection with our use of tbe specimens in the United States Na- 
tional Museum. To Dr. Bean, in particular, we have been indebted for 
help of various sorts, including many unpublished notes. To Dr. Theo- 
dore Gill and to Prof. E. D. Cope, we are indebted for numerous aids 
and suggestions. Mr. Samuel Garman, of the Museum of Comparative 
Zoology, has given us considerable assistance on the Elasmobrauchs. 
Mr. Chas. L. McKay, of the United States Signal Service, has revised 
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