264 
ERIK A : SON STENSIO 
The dorsal fin (Z), PI. 28, fig. 3 ; PL 33 ; PL 34, fig. 2; Pl. 35, figs. 1, 3 ) is somewhat 
larger than the anal fin, but has about the same shape as this. Its anterior margin 
corresponds on the ventral side to a point situated about half-way between the ventral 
fins and the anal fin; its posterior part is opposite the latter fin. The lepidotrichia are 
14—15 in number. They decrease uniformly in length posteriorly and are also developed 
in other respects in the same way as those of the anal fin. The fulcra are strong 
and numerous. 
The endoskeletal radials of the dorsal fin are represented by a row of long bone 
elements ( Rd , Pl. 28, fig. 3 ), which follow about 2— 3 mm proximally of the bases of the 
lepidotrichia. These elements may correspond to at least the proximal segments of the 
radials and perhaps also to the middle ones (cf. Schmalhaussen, 1912, igi 3 a, igi 3 b). 
On the other hand the distal ones were undoubtedly cartilaginous and, as usual, small. 
It is specially noteworthy that the endoskeletal radials corrospond exactly or 
almost exactly in number to the lepidotrichia, a condition which we shall see is also 
the case in the other forms included by me among the Catopterids. This agreement in 
the number of lepidotrichia and endoskeletal radials is of morphological importance 
inasmuch as it shows that a specialization of the musculature has taken place in the 
direction of the conditions in higher ganoid forms and Teleosts (cf. Schmalhaussen, 1912, 
igi 3 a, igi 3 b). Palaeoniscids, Platysomids; *) Chondrosteids, Acipenserids, Polyodontids 
and Saurichthyids in general show, as we know, primitive conditions in this respect 
(cf. Traquair, 1877 a, p. 27; 1879, p. 386 ; Woodward, 1890 a, pp. 15, 16; 1891b, p. 427, 
1895b, pp. 11, 27; 1898 a, pp. 84, 89—90, 92, g 3 ; Goodrich, 1909, pp. 211 — 212, 3 o 8 
— 3 og, 32 i; etc.). 
The caudal fin is incompletely preserved in all the present specimens. It is, however, 
distinctly observable that it was abbreviate-heterocercal or fairly homocercal. Its lepido¬ 
trichia are relatively fine and closely jointed right down to the base. Fulcra can be 
observed, at least on the ventral lobe. 
All the lepidotrichia, both in the paired and unpaired fins, were covered with ganoine. 
The skeleton of the shoulder girdle and the paired fins. 
Of the shoulder girdle only the membrane bones are known. Of these the cleithral 
{Cl, Pl. 34, figs. 1, 2) was developed about as in the Palaeoniscids with a high posterior 
shank, situated vertically and a shorter anterior one which is fairly horizontal. The 
supracleithral ( Scl, Pl. 34, figs. 1, 2; Pl. 35, fig. 1) is high. The suprascapular seems to 
be represented by a comparatively large oval plate ( Sscap, PL 33 ). The claviculae were 
probably present, although they were of course small; only insignificant remains of 
them are preserved {Id, Pl. 34, figs. 1, 2) in one specimen (P. 177). * 2 ) Immediately behind 
the posterior shank of the cleithrum we find, as in certain Protospondyli (Lepidotus? 
*) An exception from this is found in the so-called Platysomus canadennis Lambe (1914, pp. 17—23) where 
the lepidotrichia and endoscheletal radials are said to the present in equal numbers. 
2 ) In Colobodus maximusl have found claviculae, and Stolley (1Q20, p. 36) considers that he too observed 
them in C. konigi, but I am not convinced that his view is correct, at least to judge from his figure 5 on Pl. XI. 
— In this connection it is worth adding that I found rudiments of claviculae in Lepidosteus too, where they seem, 
to occur rather often. 
