io8 
ERIK A : SON STENSIO 
With regard to dentition and the strong development of the sensory canals this 
genus resembles Axelia, as has already been pointed out above. The pterygoid also has 
many features in common in the two genera, though at the same time it shows rather 
great differences. The chief characteristics of Mylacanthus , as far as we know, are the 
lobed or spiny postero-ventral margin of the opercular and the high shape of the 
metapterygoid, quadrate and posterior pterygoid limb. With regard to the scale sculpture 
Mylacanthus resembles Libys to some extent. 
Mylacanthus lobatus n. sp. 
(Pi. 18, figs, i, 4 ). 
There are only three incomplete specimens of this species ( P. 216- — 218), with 
remains of the visceral skeleton and a number of scales. To judge from the specimens 
present, M. lobatus seems, with regard to size, to correspond 
approximately to W. sinuosa or it has perhaps been some¬ 
what larger than this species. 
Visceral skeleton. 
The pterygoid ( Pt , text fig. 50; PL 18, fig. 4) most 
closely resembles that of Axelia in its general configuration, 
but the posterior limb is strikingly narrower and higher, 
the anterior one, on the contrary, considerably lower or 
— to express it in another way — the anterior limb does 
not reach so far upwards along the anterior border of the 
posterior limb as in the Axelia species. The upper margin 
of the posterior limb is characterized by having a very 
deep sinus, which at is lower part even comes ventrally 
of the antero-ventral corner of the metapterygoid bone. 
The quadrate ( Qu , text fig. 50; PI. 18, fig-. 4) is ex¬ 
ceedingly powerful and thick and also high. Its dorsal part 
covers in the usual way the postero-ventral corner of the 
pterygoid from the lateral side. It reaches considerably farther ventrally than was the 
case, for instance, in Axelia. In addition the corpus and the anterior lamella on it are 
distinguished in the usual way, as has been described in A. robusta. The corpus does 
not consist of compact bone in its dorsal half, but it has undoubtedly been cartila¬ 
ginous in its interior. Farthest dorsally only a fairly thin perichondral layer of bone 
seems to have been present. 
The metapterygoid ( Mptg , text fig. 50) is rather higher than broad. In other respects 
it has the usual shape, with a concave dorsal and almost straight, anterior margin. 
The caudal and ventral margins are strongly convex and pass into each other without 
any very distinct boundary. The anterior upper corner is less drawn out than in both 
A. robusta and W, sinuosa. 
Of the substitution bones of the Meckelian cartilage only one, the autangular 
(.Aang , PI. 18, fig. 4) is present, though poorly preserved. It forms the most posterior 
corner of the lower jaw and is undoubtedly identical with the bone denoted by Woodward 
Mylacanthus lobatus n. sp- 
The bones of the palato-quadrate, with 
the exception of the autopalatine, in 
lateral view. 
From P. 217 and P. 218. 7,. 
Mptg, metapterygoid; Pt, pterygoid; 
Qu, quadrate. 
