THREE-BEARDED ROCKLING. 
551 
whether he really distinguished between it and Linnaeus's Garlits medi- 
terraneus, and he was evidently doubtful himself on this point. Still, 
when lie says that it is more common in the Atlantic on the coast of 
Cornwall than in the Mediterranean and the Adriatic, he undoubtedly 
refers principally to our species. Bloch’s description and figure (Ausl. 
Fische , Th. II, p. 100; pi. CLXV) are no less obscure; but the 
names of Three bearded cod in Pennant and Gadus tricirratus in 
Donovan (1808) defend Nilsson’s Motella tricirrata. 
Risso ( Eur . Mer.) distinguished between three Mediterranean 
species of this genus ( Onos mustella, On. ma'culatus, and On. fuscus ), 
but based this distinction on the chromatic characters alone. Costa 
(Fn. Regn. Nap., Pesci , Malacott., Sottobr., pp. 17 and 39, tav. 
XXXVIII, bis) recognised only two, one ( Motella communis ) corre- 
sponding to Risso’s Onos fuscus, the other to the Onos maculatus of 
the latter and coinciding with Linnaeus’s Gadus mediterraneus (Syst. 
Nat., X, tom. I, p. 255; Mvs. Ad. Frid., tom. 1 1 : d i prodr., p. 60). 
The latter species was described by Canestkini (Arch. Zool., Anat., 
Fisiol., vol. II, p. 369, tav. XV — XVI, fig. 2) from the Gulf of Genoa, 
under the erroneous name of Motella communis. Collett, Lutken, 
and Lilljeborg give true form- characters to distinguish between two 
Mediterranean species, the one identical with the Three-Bearded Rock- 
ling, the other with Linnaeus's Gadus mediterraneus. Moreau, like 
Risso, but on better grounds, distinguished between three Mediterranean 
species: Motella tricirrata (Risso’s Onos mustella ), Motella maculata 
(i Onos maculatus , Risso), and Motella fusca ( Onos fuscus, Risso). On 
the chromatic character we can hardly pass any opinion, for the only 
specimens we have been enabled to examine were preserved in spirits®. 
The form-characters, on the other hand, show an extremely close con- 
nexion between the three species. In most characteristics Onos fuscus 
is an intermediate form between Onos mediterraneus and Onos tri- 
cirratus, thus impairing the validity and usefulness of these charac- 
teristics. This is the case for example with the difference pointed 
out by Moreau in the length of the upper jaw from the tip of the 
snout to the hind extremity of the maxillary bones. In our speci- 
mens of Onos mediterraneus this length is exactly 1 / 2 , in the speci- 
mens of Onos fuscus 5 1 1 /., — 52 %, and in those of Onos tricirratus 
53 — nearly 58 %, of the length of the head. Again, as far as we 
can judge from our materials for examination, the breadth of the inter- 
orbital space in Onos mediterraneus is less than 30 %, in On. fuscus 
more than 30 but less than 33 %, and in On. tricirratus more than 
35 % , of the postorbital length of the head. The length of the upper 
jaw in On. mediterraneus is less than 30 %, in On. fuscus more than 
30 but less than 34 %, and in On. tricirratus more than 34 %, of 
the distance between the second dorsal fin and the tip of the snout. 
The length of the lower jaw in On. mediterraneus is less than 33 %, 
in On. fuscus more than 33 but less than 36 /, and in On. tricir- 
ratus more than 38 /, of the distance just mentioned. The length 
of the base of the first dorsal fin in On. mediterraneus is more than 
74 °/o, in On. fuscus less than 70 but more than 66 %, and in On. 
tricirratus less than 63 %, of the distance between the first dorsal 
fin and the tip of the snout. Onos fuscus occupies this intermediate 
position in spite of the fact that, according to Moreau, it never at- 
tains the same size as the two other species, a circumstance which 
is especially worthy of remembrance in the case of the specimens we 
have examined, among which the specimens of Onos fuscus are almost 
exactly equal in size to the youngest specimens of Onos tricirratus. 
In the characters which show distinct changes of growth common to 
all three species (rising or falling jiercentages as expressions of the 
relative proportions of form), this intermediate position should thus 
be explained as the expression of a more advanced development at a 
smaller size in the case of On. fuscus. But in some respects the 
intermediate position does not hold good, and On. fuscus ranks beside 
the younger specimens of On. tricirratus, or takes a lower place in 
the scale of development than they. This is the case for example 
in the relation between the breadth of the interorbital space and the 
least depth of the tail, a relation which, though it does not afford 
any constant characteristic difference, still shows distinct changes of 
growth. In other relations again, as for example in the least depth 
of the tail expressed in proportion to the distance between the second 
dorsal fin and the tip of the snout, where we have a constant di- 
stinction between On. tricirratus and the other two species, On. fuscus 
stands nearer On. mediterraneus. Finally, in other relations, in which 
the direction of development is different in On. mediterraneus and 
On. tricirratus, On. fuscus, like the early stages of these two spe- 
cies, points still more distinctly to the original starting-point common 
to the development of the other two species. As an example of 
this we may take the relation between the postorbital length of the 
head and the distance between the second dorsal fin and the tip of 
the snout. This length, expressed in percent of the said distance, 
relatively decreases with increasing age in On. mediterraneus , but 
increases in On. tricirratus, according to the following results of our 
measurements: 
Specimens fro m 
(T) 
CIO 
3 1 
5" ° 
5 o 
£ « 
ns 
Least breadth of the 
interorbital space in 
% of the least depth 
of the tail. 
Least depth of the tail 
in % of the distance 
between the second 
dorsal fin and the tip 
of the snout. 
Postorbital length of 
the head in % of the 
distance between the 
second dorsal fin and 
the tip of the snout. 
Onos 
mediterraneus . 
co .Jr 
2 S 
rf. v ' 
Onos 
tricirratus. 
C5> 
ft. 
§' O 
- © 
ft Co 
3 
Si 
Onos 
fusctis. 
Onos 
tricirratus. 
© 
ft. 
cS* o 
*5 3 
3 © 
© 
1 ^ 
'StntDdMOMf 
SOUQ 
Island-belt of Gothenburg, through A. Stuxbeug. 
430 
_ 
65.fi 
23.9 
42,i 
Bergen, through the Museum of Upsala University, cf - 
360 
— 
— 
70. o 
— 
— 
22.7 
— 
— 
41.8 
Nice, through T. Thorell, specimen in possession of the Museum of Upsala University.. 
293 
— 
— 
77.7 
— 
— 
19.i 
— 
— 
41.5 
Locality unknown, from the Payroll Collection in the Royal Museum... 
246 
60. o 
— 
— 
15.o 
— 
— 
34.9 
— 
— 
Algiers, the property of the Museum of Upsala University 
232 
64.o 
— 
— 
16.2 
— 
— 
36.3 
■ — 
— 
Mediterranean, Linnaeus’s type-specimen, from Drottningholm Museum 
189 
66.o 
— 
— 
14.7 
— 
— 
37.7 
— 
— 
Naples, through the Zoological Station, cf 
176 
— 
76.i 
— 
— 
17.3 
— 
— 
40.2 
— 
Nice, through T. Thoreli, 
171 
— 
— 
76.2 
— 
— 
19.i 
— 
— 
41.4 
Naples, through the Zoological Station, $ . 
164 
— 
81.2 
— 
— 
15.5 
— 
— 
39.4 
— 
Nice, through T. Thorell 
160 
— 
— 
71.4 
— 
— 
20. o 
— 
— 
39.4 
a It is a known fact, however, that young Three-bearded Rocklings at the termination of the Couchia-penoc] are of a plain reddish 
brown colour, darker or lighter, and do not show any traces of spots until they have attained a more advanced age. 
