CUIRASSED GURNARDS. 
203 
Gurnards. But the absence of the air-bladder, the 
undivided pectoral tins without free rays at the bottom, 
the somewhat singular form of the bod) 7 , and the situa- 
tion of the vent, which lies far in front of the end of 
the abdominal cavity, nearer the ventral fins than the 
anal tin, are all in favour of the procedure of Gill", 
and after him of Jordan and Gilbert 6 , who isolated 
these fishes under the family name of Agonidce , which 
was first employed by Swainson 1 '. The body is of the 
typical Cottus form, with the head thicker than the 
body, which tapers posteriorly in a conical form, but 
is sometimes so elongated and low that, with its few 
rows of plates, it reminds us of the Syngnatlii. Its 
resemblance to the latter is further increased by the 
longitudinal curvature of the plates on the trunk, which 
are traversed by a keel at the middle, on the outside of 
the curve. Sometimes, too, as in the genus Siphagonus, 
the snout, with the projecting lower jaw, is almost tu- 
bular and resembles that of Syngnathus. Sometimes, 
however, as in the genus Bothragonus, the body is 
laterally more strongly compressed and fairly deep and 
short. The variations of form within the family are 
thus by no means inconsiderable. The eyes are set 
high, but on the sides of the angular and lacunose 
head; and on the lower part of the cheek we find the 
row of muciferous pores, belonging to the system of 
the lateral line, which we have remarked above in the 
fry of the Sapphirine Gurnard. The strange appearance 
of the head is often enhanced by the elongation of the 
snout into a kind of proboscis, and by the spines on the 
upper surface of the latter; and numerous barbels are 
sometimes attached to the lower side ol the head. 
Behind the fourth branchial arch the gill-slit has dis- 
appeared; and the pseudobranchiae are well-developed. 
The jaw-teeth are small and cardiform; and similar 
teeth sometimes occur on the palatine bones and the 
vomer as well. The ventral fins, with one spinous and 
two or three soft rays, are set fairly close together 
and somewhat behind the insertions of the pectoral fins. 
As a rule, there are two dorsal fins, the anterior with 
spinous rays; but sometimes, in the genus Aspidopho- 
roides d , this last fin is wanting. 
The systematical, as well as the morphological, 
relations between the genera are explained, in this fa- 
mily as in others, by the changes of growth in the 
species, which changes have already been described by 
Steenstrup and LutkEn e . The most remarkable of 
these changes is the gradual removal in a, forward 
direction of the vent — in a specimen of Agonus de- 
cay onus, 76 mm. long, from Greenland, we find 8 pairs 
of plates between the vent and the beginning of the 
anal fin, in another, 162 mm. long, 10 plates on the 
left side and 11 on the right; in a specimen of Agonus 
cataphr actus , 93 mm. long, from Bolmslan, there are 
5 plates on the right side and 6 on the left, between 
the vent and the anal fin, in a specimen 121 mm. long, 
6 on each side, and in a specimen 178 mm. long, 7 
pairs of plates on this space. Another change lies in 
the elongation of the tip of the snout, and the eleva- 
tion, or even the protrusion, of the nasal spines. Young 
specimens are without the marked elongation of the 
nasal bones in a forward direction, in front of the 
original tip of the snout, or even (as in Agonus decago- 
nus juv. — Ag. spin o sis simus) have the lower jaw more 
protruded than the upper. The form of the body in 
these species begins its changes with the relatively 
shorter (deeper) form in young specimens than in old, 
and with the deeper caudal region, which is even la- 
terally compressed. In young specimens of both the 
Scandinavian species of Agonus , the middle keels of the 
plates on the body and the ridges of the head are 
higher, and rise into spines pointing in a backward 
direction, even in the species (Ag. cataphr actus) which 
in the adult state can scarcely be called spinous, so 
rounded and blunt have these plates and ridges become. 
The genera which, when full-grown, are distinguished 
by the deeper form of the body, by higher spines on 
the plates, by the shorter (more obtuse) form of the 
tip of the snout or by the rising (projecting) tip of 
the lower jaw, may thus be regarded as representatives 
a Arrang. Fain. Fish., Smiths. Misc. Coll. No. 247, p. 6; Cat. Fish. E. Coast N. Amer ., ibid., No. 283, p. 2. 
b Syn. Fish. JV. Amer., Bull. U. S. Nat. Mus., No. 10, p. 722. 
c Nat. Hist., Class. Fish. Amph., Rept., (Lardn. Cab. Encycl.), vol. II, pp. 181 and 272. 
d One species of this genus, A. Olrikii, has been found both in Greenland and in Kara Sea (Lutken in Dijmphna-Togtet, p. 120), 
and may possibly occur, therefore, in the deep water otf the extreme north of Norway, though it is just as probable that its range extends 
west only from Greenland to Nova Zembla. A specimen 65 min. in length, was taken by the Vega Expedition at a depth of 18 fathoms, 
in Behring Strait (64° 52' N. ; 172° 3' W.) 
e Vid. Meddel. Naturh. For. Kbhvn 1861, p. 276. 
