CHAPTER I 

 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 Actinopteri, or Actinopterygii, suggested by 

 Professor Cope, is now generally adopted. The shorter form, 

 Actinopteri, being equally correct is certainly preferable. This 

 term (aKris, ray ; nrepov or Ttrepvg, 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, 

 n-i i ' 



