130 — ^ Ayres on the identity of 
specimen of the gobio, the principal difference he could detect 
was, in the American fish, a ** greater height of the dorsal and 
anal fins." He mentions two other points of discrepancy. 
» One of these was in regard to the first dorsal fin which, in the 
American spécimens, was about a twelfth of an inch longer 
than in the English, occasioning a corresponding decrease of 
length in the space between the first and second dorsals. 1f 
this character were constant it might be of some value ; but it 
is not. The dorsals of the gobio vary much more than the 
small fractions of an inch here referred to. In one of those 
sent me by Mr. Yarrell the interval between the first and 
second dorsals is two and a half lines, the fish being four - 
inches in length. (These are precisely the numbers stated by 
Dr. Richardson, and it is possible that the specimen now in 
my possession is the very one from which his measurements 
were taken; it certainly agrees with them in every respect.) 
In one of those received from Mr. Bolton there is no interval 
between the fins; they unite so pérfectly that the membrane 
of the first dorsal is attached to the first ray of the second to 
the height of a twelfth of an inch. In another the two fins 
unite, but not so strongly, the membrane of the first dorsal 
reaching to the base of the first ray of the second. In 
another there is an interval between the two, but it is less 
than in the first instance. And the length of the first dorsal 
varies according to the union of the two fins or the space be 
tween them. The discrepancy noted in this case is, therefore, 
of no importance. 
In regard to the height of the dorsal and i! fins it may 
observed, that the comparison was made by means 
cimens preserved in alcohol, from which the measurements 
. could scarcely be taken with so much accuracy as from the 
recent fish. I do not mean to imply that Dr. Richardson is i 
error here, for I have no means of knowing that such is. the 
fact ; but certainly, a difference amounting to but little more - 
than a twelfth of an inch, for that is the greatest — 
