INTERRELATIONSHIPS OF TELEOSTOMES 147 
than genetic kinship. The Crossopterygian, whose ancient 
structure is well known, may well have been derived from 
an ancestor common to the Ctenodont (Dipnoan) and 
Holoptychian (Fig. 153) ; so that the gradual nearing of the 
Teleostome stem to that more fixed, of the Dipnoan, is a 
strong suggestion as to its derivation. The later descent 
of the Ganoids from an ancestor closely akin to, if not 
identical with the Crossopterygian, is usually conceded. 
Teleosts first occurring in Cretaceous are by evidence of 
fossils the almost undoubted survivors of an extensive 
group of transitional Mesozoic Ganoids (p. 165). But 
whether all Teleosts are to be deduced from a single 
ganoidean phylum can at present hardly be established. 
Thus catfishes, or Siluroids, appear in many structural 
regards closely akin to the sturgeon (p. 160); but as their 
fossil remains are lacking before the Eocene—when, how- 
ever, they appear to have been in every way as highly 
evolved as in recent forms —little clue has been given to 
their descent. 
Teleostomes may, in the present connection, be briefly 
characterized under their two principal subdivisions. 
I. CrossoPpTERYGIAN, the more archaic group, uniting 
characters of shark, lung-fish, and Ganoid, retaining the 
ancient cartilaginous fin bases, radials, and basals in their 
lobate fins; in some forms (Holoptychius, Fig. 153), the 
__ concrescence of the basal parts of unpaired fins passing 
through the same evolution as those of paired fins. 
_ Represented in the surviving Polypterus (“Bichir” of 
_ the White Nile, Fig. 148), and in the slender Polypteroid 
Calamoichthys (of Calabar), and in the extinct Hofoptych- 
ius, Undina, Diplurus, and Ccelacanthus. 
II. AcrinopTeryGiAN, the spine-finned Teleostomes. 
Fins supported by dermal rays ; ancient fin support greatly 
. 
