2 12 
ERIK A : SON STENSIO 
of this process resembles that of the one found in Lepidotus (Woodward, 1893 b, p. 561, 
fig. 6) and Amia (Allis, 1897 a, PI. XX, fig\ 2). 1 ) 
Of the membrane bones of the palatoquadrate only the ecto- and entopterygoid 
are preserved. 
The ectopterygoid ( Ecpt, text fig. 70) is a narrow bone situated along the lateral 
border of the palatoquadrate and extending backwards right to the quadrate component 
of the quadrato-metapterygoid. It consists of a radiate bone substance and its centre of 
ossification is situated far forward. 
The entopterygoid ( Enpt, text fig. 70) is rather high and large. It extends so far 
dorsally that it partly covers the metapterygoid component of the quadrato-meta¬ 
pterygoid on its medial surface. Like the ectopterygoid it is built up of a radiate bone 
substance. The ossification centre is near its ventral margin rather far backwards. 
Up to now the palatoquadrate in Palaeoniscids has been very incompletely known. 
Traquair (1877 a, p. 18; 1901, p. 84; 1909, p. 118) described remains of it in a couple of 
forms (Nem atop tychins and Elonichthys), and said that in these forms it consisted of several 
ossifications, although in most cases it was impossible to establish their shape and 
extent. His statement in this connection that the quadrate and metaptejrygoid were in¬ 
dependent and not fused as in Boreosomus is of special interest. 
As Traquair is known for his accuracy and as he has, in addition, described and 
figured the quadrate and the metapterygoid as mutually independent elements in a 
Platysmoid (Cheirodus, 1879, pp. 366— 367; PI. V, fig. 10), one is not yet justified in doubting 
to any extent the correctness of his observations. Consequently, as far as we know at 
present, there probably occurred in the Palaeoniscids both forms in which the quadrate 
and the metapterygoid were independent and forms in which these two bones were fused 
with each other, as in Boreosomus. I shall have an opportunity to show below (Part II) 
that the latter conditions are found in another form (Saurichthys) among the lower Ganoids. 
The mandible (text fig. 70) is relatively robust and has the shape usual in Palaeo¬ 
niscids, i. e. it is quite without a coronoid process and its labial margin is straight. Its 
lower margin is weakly convex. Its postero-ventral corner is well rounded. 
Only one substitution bone is found in the mandible ( Mk , text fig. 70), reaching 
throughout the whole length of this from the symphyse to the posterior end. In the 
anterior two-thirds this bone is only a narrow rod, but increases considerably in height 
in its posterior third. From the lateral to the medial side it is rather thick, and it can 
be clearly seen that it consists of a cancelleous bone substance. It is principally situated 
in the dorsal half of the mandible. Only its posterior part reaches somewhat dovvn into 
the ventral half. The anterior and middle thirds of its upper surface are directly covered 
with the medial tooth-bearing lamella that issues from the upper margin of the dentalo- 
splenial. Its posterior third, on the other hand, is freely visible on the dorsal surface 
of the mandible and has an articulatory fossa for the quadrato-metapterygoid not far from 
the posterior end. In front of the articulatory fossa there follows on the lateral side of the 
bone a fairly long and rather deep niche {mg, text fig. 70), closed laterally by the membrane 
In Amia, however, this process does not articulate with the neurocranium, and it is uncertain whether it did 
so in Lepidotus. In Lepidosteus, on the other hand, an articulation is, as we know, developed between the meta¬ 
pterygoid and the neurocranium. 
