XXIII PLECTOGNATHI F25 
among fishes. According to Brown Goode, “the propelling 
force is exerted by the dorsal and anal fins, which have a half 
rotary, sculling motion, resembling that of a screw propeller; the 
caudal fin acts as a rudder, save when it is needed for unusually 
rapid swimming, when it is used as in other fishes; the chief 
function of the broad pectorals seems to be that of forming a 
current of water through the gills, thus aiding respiration, which 
would otherwise be difficult on account of the narrowness and in- 
flexibihty of the branchial apertures. When taken from the 
water, one of these fishes will hve for two or three hours, all the 
time solemnly fanning its gills, and when restored to its native 
Fic. 438.—Ostracion quadricornis. x}. 
element seems none the worse for its experience, except that, on 
account of the air absorbed, it cannot at once sink to the bottom.” 
“No group of tropical fishes,’ says the same author, “is so 
thoroughly worked out in the writings of the fathers of natural 
history as this one. Over 200 years ago every species of trunk- 
fish now taken from the Atlantic was known to and described by 
the naturalists, and it is a well-deserved tribute to their dis- 
crimination as zoologists to say that none of the many efforts 
which have since been made to subdivide their species have been 
at all successful.” 
Division I].—GYMNODONTES. 
Supraclavicle oblique, sometimes nearly horizontal; lower three 
pectoral pterygials enlarged and immovably united to the coraco- 
scapular cartilage; upper pterygial small, suturally united to the 
seapula. Anterior vertebrae with bifid divergent neural spines. 
Basis cranii simple ; suture between dentary and articular evident. 
Pelvis absent. 
The spinous dorsal and the ventral fins are constantly absent, 
the praemaxillaries are united to the mavxillaries, and the teeth 
