INTRODUCTION. IE 
tributary to Lake Erie. The species is evidently not, as believed 
by McCormick, ‘‘ restricted to a very narrow geographical range.’’ 
The cysts formed by this parasite reproducing in the subcutan- 
eous tissue may reach a diameter of one-third inch, and as many 
as eleven cysts have been noted on a single fish. It would seem 
that in some cases they must inevitably cause the death of the 
host. 
Specimens of all the species of fishes recorded by Kellicott, 
Williamson, Parker and the writer are deposited in the museum 
of the Ohio State University. 
In the preparation of this paper free use has been made of 
the works of the various writers on Ohio fishes, of ‘‘ The Fishes 
of North and Middle America’’ (Bulletin 47, U. S. National 
Museum), by Drs. David Starr Jordan and Barton W. Evermann ; 
of Dr. O. P. Hay’'s ‘‘ Lampreys and Fishes of Indiana’’ (19th 
Annual Geol. Rept. of Ind.), and of the reports and bulletins of 
the U. S. Commission of Fish and Fisheries. The classification 
is that adopted by Jordan and Evermann in Bulletin 47, U. S. 
Natl. Mus. The keys for the separation of families, genera and 
species have, for the most part, been taken from the same work, 
but modified and abridged to meet-the requirements of the more 
limited scope of this paper. The descriptions have been drawn 
largely from the same source, but as far as possible these have 
been verified for Ohio specimens, and modified as occasion 
demanded to make them apply more closely to the species as 
found in Ohio. 
While it is not the purpose to discuss in this paper the gen- 
eral anatomy of the fish, such as may be found in any good 
laboratory guide on zoology, a few hints to the beginner in 
regard to methods of procedure and to some particular points of 
structure may here finda place. The teeth in some species are 
borne on nearly all parts of the mouth and pharynx—premaxil- 
laries, maxillaries, mandibles, vomer, palatines, tongue, hyoid 
apparatus, pterygoids and pharyngeals, but may be wanting from 
any or allof them. The examination of all but the last men- 
tioned can usually be satisfactorily made through the open mouth 
by using a blunt dissecting needle or the head of a pin as a 
“‘feeler.’’ It is the determination of the number and arrange- 
