PREFACE. 
I nAvE selected the Artedian genus Cottus as the subject of my first monograph, 
on account of the interest which attaches to the questions involved in its investi- 
gation. The first of these questions is to ascertain whether there really exists but 
one single species of the genus in Europe, and another in America. The second, 
whether indeed the same species is common to both countries, as was at one time 
supposed. 
My investigations embrace, and, I hope, solve both of these questions. The 
materials made use of are numerous and of special value; some of them absolutely 
essential to the proper determination of the above-mentioned points. 
As far as it has been in my power, I have consulted the original documents, and 
their authors themselves. Thus I owe to Professor S. 8S. Haldeman an authentic 
individual of his ©. viscosus. Through the kindness of Professor James Hall, of 
Albany, I have studied the specimen drawn and described by Dr. De Kay under 
the name of Uranidea quiescens, which proved to be a true Cottus. Mr. W. 0. 
Ayres has placed in my hands specimens of his C. gobio from the State of Con- 
necticut. From information communicated by Dr. J. P. Kirtland, of Cleveland 
(Ohio), I have identified his C. gobio. Rey. Z. Thompson, of Burlington (Vt.), has 
sent me a species hitherto undescribed. Specimens caught near the White Mount- 
ains were communicated by Dr. D. Humphreys Storer. I have made a complete 
study of the species brought by Prof. Agassiz from Lake Superior. 
In examining the collection of fishes in the Academy of Natural Sciences of 
Philadelphia, with the assistance of Dr. J. Leidy, I found one specirhen by which I 
became fully satisfied of the existence of two species in the tributaries of the Ohio 
River. But the most important contributions have been from the collection of 
Professor 8. F. Baird, now at the Smithsonian Institution. Numerous specimens of 
C. viscosus and others have enabled me to give the anatomical details contained in 
Chapter IT. : 
I beg all these gentlemen to accept the assurance of my deepest gratitude, and 
to receive my labor with the same indulgence which they have shown towards me 
during its elaboration. 
Most of my descriptions rest upon the examination of numerous specimens: a 
few of them are drawn from one individual, but the species will appear distinct 
enough to be justified. 
