480 
SCANDINAVIAN FISHES. 
pen, changed it to Gad us ogat. So close is the con- 
nexion between this species and Gadus callarias that 
most recent writers have identified it with the latter. 
Dressel", however, refers us to his measurements of four 
specimens of G. ogac and the same number of G. cal- 
larias, and gives the following specific characters: in 
G. ogac the peduncle of the tail is shallower, the eyes 
and the interorbital space larger, the barbel longer, the 
ventral fins set farther forward, and the pectoral fins 
longer, than in G. callarias. 
The Dicksonian expeditions to Greenland have put 
the Royal Museum in possession of four specimens of 
Gadus ogac, between 294 and 566 mm. long, which 
show that most of the characters given by Dressel lose 
their validity when compared with the numerous changes 
of growth in Gadus callarias. One of these characters, 
however, that which is drawn from the relative breadth 
of the interorbital space, and is adopted in our table 
for the distinction of the species within this genus, has 
proved universally true. This character, as well as the 
difference that appears in the average position of the 
ventral fins, is of great interest in our fauna, for, though 
the Baltic Cod never attains quite the same point as 
ogac in this respect, still it comes much nearer the 
latter, on an average, than the oceanic Cod does. 
In the Cod the breadth of the interorbital space 
increases even relatively during growth, rising in pro- 
portion to the length of the body, according to our 
measurements of Cod from the Cattegat and Skager 
Rack, from 5'9 % in specimens on an average 142 mm. 
long to 6’9 % in specimens on an average 462 mm. 
long. In the Baltic Cod that we have measured, the 
latter percentage appears in specimens of an average 
length of 422 mm., and in our specimens of G. ogac, 
of an average length of 435 mm., this proportion is on 
an average 8‘4 %. In this relation, however, the charac- 
ter is not constant, for in macrocephalic Cod the per- 
centage may rise to at least 9; but it becomes constant 
if we compare the breadth of the interorbital space with 
the length of the head, when we obtain the following 
average results: 
Average length 
of the body 
in mm. 
Average least 
breadth of the 
interorbital space 
in % of the length 
of the head. 
In Cod from the Cattegat and Skager Rack 
101.5 
21.8 
11 11 11 11 11 11 11 11 
203.5 
22.4 
11 11 11 11 11 11 11 11 
265.5 
22.9 
11 11 11 11 11 11 11 11 
461.6 
23.3 
,, ., ,, Baltic „ ., ,, 
422.0 
24. c 
„ Gadus ogac 
434.5 
30.i 
In accordance with the general rule for the changes 
of growth of the Teleosts, that the ventral fins move 
more and more forward, the distance between the fore- 
most (outermost) point of the insertions of these fins 
and the beginning of the first anal fin shows a per- 
sistent increase during growth in the Cods, when com- 
pared with the length of the body. The length of the 
base of the first anal fin also persistently decreases in 
comparison with the distance between this fin and the 
ventral fins. In these respects too, Gadus ogac is most 
advanced in development, though the Baltic Cod show 
a distinct tendency towards the same point. 
Average length 
of the body 
in mm. 
In Cod from the Cattegat and Skager Rack 
11 11 11 11 11 11 11 
11 11 11 11 11 11 ?? 11 
„ ,, ,, „ Baltic „ „ 
„ Gadus ogac 
89.4 
192.0 
4(38.3 
422.0 
434.5 
Averag 
e distance 
between 
the inser- 
tions of 
the ventral 
fins and the be- 
ginning 
of the first 
anal fin 
in % of the 
length of the body. 
Average length of 
the base of the first 
anal tin in % of the 
distance from the 
insertions of the 
ventral fins to the 
beginning of the 
first anal fin. 
19.2 
21.2 
24.1 
26.1 
29.7 
93.9 
91.1 
74.8 
74.2 
62.3 
Proc. U. S. Nat. Mus., vol. VII, p. 246. 
