206 
SCANDINAVIAN FISHES. 
R. hr. 6; D* 7|G — 8 ; A. h 7 1. 8; P. c 16; V. l / 2 ;C. d x + 7 + «; 
L. lat. por. e 25 — 29. 
Syn. Cottus cataphractus , Fabk., Fn. Groenl., p. 155 (nee Lin.). 
A g onus decagonus, Bl., Syst. Ichthyol., ed. Sohn., p. 105, tab. 
27; Cuv., Val., ( Aspidopliorus ) Hist. Nat. Poiss., IV, p. 223; 
Reinh., Dan. Vid. Selsk. Naturh., Math. Afh., V, 'Overs. 1829 
— 1830, p. LIII; ibid. VII, pp. 114 et 119; Kb., Naturh. 
Tidskr. Kbhvn, ser. 2, vol. I, p. 243 ; Id., Voy. Scand., Lapp., 
Gaim., Poiss., tab. 5, fig. 1; Nilss., Skand. Fn., Fisk., p. 88; 
Gthr, ( Agonus ) Cat. Brit. Mus., Fish., II, p. 215; Mgkn, 
( Aspidopliorus ), Finl. Fislefn., (disp.), p. 12; Id., Ofvers. Vet.- 
Akad. Forh. 1867, p. 260; Gill, ( Archagonus ) Cat. Fish. E. 
Coast. N. Ainer., Smiths. Misc. Coll., No. 283, p. 22; Coll., 
(Agonus), Vid. Selsk. Forh., Chrnia 1874, Tilltegsh., p. 40; 
Ltkn, Vid. Meddel. Naturh. For. Kbhvn 1876, p. 381; Coll., 
Norske Nordh. Exped., Zool., Fiske, p. 44, tab. II, fig. 11 
et 12; Lillj., Sv., Norg. Fisk., I, p. 193; Jobd. (Agonus, 
Podothecus) Proc. Acad. Nat. Sc., Philad., 1883, p. 293. 
Aspidopliorus spinosissimus , Kb., Naturh. Tidskr., 1. c., p. 250; 
Voy. Scand., 1. c., fig. 2; Gill ( Leptagonu.s ), Proc. Acad. 
Nat. Sc. Philad. 1861, p. 167; — form. juv. demonstr. 
Steenstr., Ltkn, Vid. Meddel. Naturh. Forh. Kbhvn 1861, 
p. 280 . 
Aspidopliorus malarmoides, Eud., Desl., Mem. Soc. Linn. 
Norm., tom. 9, p. 167. 
According to the above remarks on the mutual re- 
lations of the forms within this family, Agonus decagonus, 
in form of body, occupies a higher place in the scale 
of development than the following species; but in most 
other respects it remains at a lower stage. The former 
character is most clearly expressed, as usual, by the 
proportions of which the least depth of the tail is a 
factor; and, connected with the elongated form of the 
body, we find the comparatively large number of plates 
in the longitudinal rows. These rows are anteriorly 8 
in number, but on the tail, a little behind the second 
dorsal and the anal fin, are reduced to 6, owing to the 
confluence of the two neighbouring rows on the back 
and the under side of the tail. On the back there are 
5 or 6 plates in front of the first dorsal fin, -which 
itself extends along 8 or 9 plates; then 3 or 4 (some- 
times 5 according to Collett) similar pairs of plates 
between this fin and the second dorsal, which generally 
extends along 7 plates. Behind this point 2 pairs of 
plates may generally be distinguished, and then the 
two rows coalesce, at first retaining a- longitudinally 
divided, superior ridge on the plates, the number of 
which we have found to be 18 or 16 (from 14 to 17 
according to Lutken) in this simple dorsal row to the 
base of the caudal fin. The anterior part of the lateral 
line of the body is furnished with about 5 (in young 
specimens) or 7 (in old) smooth, scaly plates, which it 
pierces in the ordinary way; and during this part of 
its course the lateral line slopes down from the upper 
corner of the gill-opening almost to the middle of the 
side, vertically below the beginning of the first dorsal 
fin, the point at which the upper of the two lateral 
rows of spinous plates begins, while the lower has al- 
ready begun at the middle of the axil of the pectoral 
fin. The lateral line now rounds the upper lateral row 
of plates and runs along the middle of the side to the 
base of the caudal fin. At the beginning of its course 
between the two lateral rows of plates it still opens 
into a pore at each of the first two (perhaps three) 
plates; but then these ducts become elongated and run 
in the form of small lateral tubes along the lower side 
of the lateral line proper, opening only at every second 
or every third plate. Hence it follows that when, for 
example, we can count 42 spinous plates in the lower 
lateral row, we can find only 29 pores in the lateral 
line. On the head the system of the lateral line is 
furnished with large muciferous pores, both under the 
lower margin of the suborbital bones and in the lower 
posterior margin of the preoperculum, where four cor- 
ner-spines (most distinct in young specimens) — the 
uppermost (hindermost) pointing backwards and upwards, 
the corner-spine itself backwards and downwards, the 
next downwards, and the first one forwards and down- 
wards — form the boundaries of the muciferous pores 
between them, which are continued, as usual, in a row 
on the lower side of the branches of the lower jaw. 
The anterior nostrils are fairly large, cylindrical, der- 
mal ducts, turned outwards and set about half-way 
along the snout; the posterior, on the other hand, are 
extremely small and very slightly raised ducts, set just 
in front of the lower part of the anterior osseous boun- 
dary of the orbit (the ectetlimoid bones). Just in 
front of the posterior nostrils lies a small round hole 
or slightly raised, opening pore of the large muciferous 
canal which belongs to the system of the lateral line 
on the head. This canal is a continuation, on each 
side of the snout, of the frontal and occipital mucifer- 
° D x . 5 or 6, according to Lutken; 5 — 7, according to Collett. 
b A. 5 — 8, according to Lutken. 
c P. 14 — 16, according to Collett. 
d All the rays simple; 3 — 5 supporting rays above, and 2 or 3 below the 7 middle rays. 
e L. lat. por. 23—25, according to Collett. 
