CHAPTER XVIII 
THE GANOIDS 
UBCLASS Actinopteri. — In our glance over the taxon- 
omy of the earlier Chordates, or fish-like vertebrates, 
we have detached from the main stem one after an- 
other a long series of archaic or primitive types. We have first 
set off those with rudimentary notochord, then those with retro- 
gressive development who lose the notochord, then those with- 
out skull or brain, then those without limbs or lower jaws. 
The residue assume the fish-like form of body, but still show 
great differences among themselves. We have then detached 
those without membrane-bones, or trace of lung or air-bladder. 
We next part company with those having the air-bladder a 
veritable lung, and those with an ancient type of paired fins, 
a jointed axis fringed with rays, and those having the palate 
still forming the upper jaw. We have finally left only those 
having fish-jaws, fish-fins, and in general the structure of the 
modern fish. [For all these in all their variety, as a class or 
subclass, the name Actinoptert, or Actinopterygii, suggested by 
Professor Cope, is now generally adopted. The shorter form, 
Actinoptert, being equally correct is certainly preferable. This 
term (axrtis, ray; mrepov or mrepvé, fin) refers to the structure 
of the paired fins. In all these fishes the bones supporting 
the fin-rays are highly specialized and at the same time con- 
cealed by the general integument of the body. In general 
two bones connect the pectoral fin with the shoulder-girdle. 
The hypercoracoid is a flat square bone, usually perforated 
by a foramen. Lying below it and parallel with it is the irregu- 
larly formed hypocoracoid. Attached to them is a row of bones, 
the actinosts, or pterygials, short, often hour-glass-shaped , 
which actually support the fin-rays. In the more specialized 
forms, or Teleosts, the actinosts are few (four to six) in number, 
246 
