INTRODUCTION. "3 
of the dorsal fin to the lateral line and from the lateral line to the 
middle of the belly. Thus the formula, ‘‘ 6—45-4,’’ means that 
there are forty-five scales in a longitudinal row, and that there are 
six rows above the lateral line and four below it. If the lateral 
line were absent the formula would read, ‘‘45-10.’’ Variations, 
sometimes considerable, may be looked for in the scale formula. 
The gill membranes (free folds of skin below the opercles, sup- 
ported by one or more branchiostegal rays) may be “‘ connected,’’ 
that is, united together in a fold below the ‘‘isthmus’’ or space 
between the throat and breast, they may be “‘joined to the 
isthmus’’ along their lower edges, or they may be “‘free’’ from 
the isthmus and from each other. The pre-maxillaries are ‘‘ pro- 
tractile’’ when they are separated in front from the skin of the 
forehead by a transverse groove, and ‘‘not protractile’’ when 
such transverse groove is incomplete or wanting. In some fishes, 
as in the bass and many sunfishes there is a ‘‘ supplemental max- 
illary’’ bone lying along the upper side of the maxillary. In 
taking body measurements the depth is taken at the deepest 
place, and the head is measured from point of snout to the end of 
the opercle, except that in sunfishes the soft flap is not measured. 
Depth and length of head are compared with the length of the 
whole body exclusive of the caudal fin. Thus, ‘‘ head 4’’ means 
that the length of the head is contained four timesin the length of 
the body. ‘The eye is measured to the full width of the orbit. 
“The writer desires. to express his gratitude to the Depart- 
ment of Zoology of the Ohio State University for the use of a seine 
and other collecting apparatus, to Prof. Herbert Osborn for 
kindly advice and assistance in many ways, and to the Trustees 
of the Ohio State Academy of Science for pecuniary aid, through 
the Emerson McMillin fund, in carrying on the work of seining. 
Special acknowledgment is also due to Messrs. J. S. Hine, W. R. 
Rhoades, Chas. Carter, F. L. Landacre, J. H. Pumphrey, S. E. 
Rasor, Chas. Osburn, and others, who by kindly assistance in 
various ways have so materially aided in the pursuit of the work. 
