127. OSTRACIID^ OSTRACIUM. 
853 
vertical slit, below aud behind the eye. Dorsal fin single, short, with- 
out spine; anal short, similar to dorsal; caudal rounded; no ventral 
fins; vertebrce 14, the anterior elongate, the last five extremely short; 
no ribs. Genera two; species about 20; chiefly of the tropical seas. 
“The locomotion of the trunk-fishes is very peculiar. The propell- 
ing force is exerted by the dorsal aud anal fins, which have a half 
rotary, sculling motion, resembling that of a screw-propeller; the cau- 
dal 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 inflexibility of the branchial apertures. 
lYlien taken from the water, one of these fishes will live for two or 
three hours, all the time solemnly fauuiug its gills, aud when restored 
to its native element seems none the worse for its experience, except 
that, on account of the air absorbed, it cannot at once sink to the bot- 
tom” {Goode). 
{Scleroderini, group Ostraciontina, Giinther, viii, 255-263.) 
a. Carapace formiug a continuous bridge behind anal fin; ventral surface not cari- 
nated Ostracium, 475. 
476.— OSTK ACini ^inn®us. 
{Ostracion, Artedi; Linnfeus Syst. Xat. x, 350, 1758: type Ostracion cuhicus Linnaeus.) 
Trunk-fishes with trigonal, tetragonal, or pentagonal carapace, the 
ventral surface never carinated; carapace closed behind the anal fin. 
Temperate and tropical seas; the trigonal species confined to the west- 
•ern Atlantic. (oVr^a'ztwv, diminutive of offr/jdzov, any hard object, like the 
shell of a mollusk.) 
a. Body three-angled. (Zactc»p/ir^« Swainson.) 
b. No supraocular spine. 
1316. O. trigroailim Linn. — Trunk-fish. 
Uniform brown, with numerous irregularly grouped whitish spots, 
most abundant on caudal peduncle; young specimens with a black 
blotch on sides behind gill-openings. Body three-angled; no spine 
before eyes. Each ventral ridge with a large, flat spine; dorsal ridge 
high and sharply compressed, descending rather rapidly forward aud 
ending opposite posterior margin of orbit ; carapace open behind the 
dorsal fin. Head 4 in length; height of sides 2. D. 10; A. 10. Y est 
Indies; occasional on our coast southwartl. 
(Linuffius, Syst. Xat. x, 330', 1758; Gunther, viii, 256; GoodC, Proc. U. S. Nat. Mus. 
1879, 276: Lactophrys trigonus Poey, Mem. Hist. Nat. Cuba, ii, 362, 1861.) 
