34 MONOGRAPH OF THE FRESH WATER III. 
account of its minuteness. In Acanthocotti, however, it is quite large and easily 
distinguishable. 
The body is smooth and deprived of scales; it is more or less viscous or slimy, as 
all fishes generally are. It diminishes gradually in thickness and in height from 
the head towards the tail. The back is almost straight or slightly arched. The 
lateral line exhibits in its structure a peculiarity which seems to belong chiefly, if 
not exclusively, to all the American species. The subcutaneous cartilages disappear 
on the last fourth of the line, whence it is continued to the base of the caudal fin 
by a series of minute pores, subjected to a sudden fall on the peduncle of the tail. 
This character had already struck Mr. Heckel, who makes of it the distinguishing 
mark of his C. gracilis, the only American species of which he saw specimens. 
Another character, more or less general, making a distinction between the species 
of the two hemispheres, is the fact that the rays of the fins have a tendency to be 
more bifurcated in the species of the old hemisphere than in those of the new. 
As far as the rays of the pectoral fins are concerned, we know only one American 
species, the C. Wilsonii, in which the upper ones are subdivided. Except in C. 
Richardsonii, where we have noticed some rays of the centre of the second dorsal 
as showing a slight bifurcation at their summit, we are not aware of any other fin 
where that character of the bifurcation of the rays exists, except in the rays of the 
caudal fin generally, although in a less degree than among the European species. 
The first dorsal fin is always lower than the second; sometimes continuous with 
the latter by a membrane, sometimes completely separated by a short interval. 
The length of the pectorals varies according to the species; their inferior rays are 
shorter and thicker than the upper ones, and their tips extend beyond the mem- 
brane which unites them, giving to the lower edge of the fin a scalloped appearance. 
There is, in the structure of the ventral fins, a peculiarity worthy of notice, and 
which will undoubtedly have a great weight upon the question of the validity of 
the species in this genus. In some there are four soft and articulated rays, whilst 
others have but three, all of them possessing the anterior short and spiny ray, 
closely connected with the first soft one and hidden in the thickness of the skin, 
Now the European species, mentioned by Mr. Heckel, are all provided with four 
soft rays to the ventrals, and this also must have struck him as an interesting 
fact, since the presence of three soft rays constitutes the second character by which 
he distinguishes his C. gracilis from all others. The study of the American species 
has taught us that this character had more than a specific value; and, in consult- 
ing the various documents respecting the history of European species, we became 
satisfied that the same was the case with regard to these latter. Some may sup- 
pose this character to be sexual, but we are convinced that it is not the case, 
having had this question before us from the very commencement of our investiga- 
tions. Having had series of individuals, young and adult, of most of the species, 
we always found it constant. Six species have four soft rays: C. cognatus, of 
Great Bear Lake; C. Richardsonii, of the northern shore of Lake Superior; C. 
Alvordii, of Lake Huron; C. Bairdii, of the north-western tributaries of the Ohio ; 
C. Wilsonii, of the south-eastern tributaries of the same river; and C. meridionalis, 
from James River (Va.). Now, if we have to deal with a sexual character, we 
