127. OSTEACIID^E OSTRACIUM. 853 



vertical slit, below ami behind tlie eye. Dorsal fin single, short, with- 

 out spine; anal short, similar to dorsal; caudal rounded; no ventral 

 fins; vertebrae 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 and 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. 

 When taken from the water, one of these fishes will live for two or 

 three hours, all the time solemnly fanning its gills, and 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). 



(Sclerodermi, group Ostraciontina, Giinther, viii, 255-268.) 



a. Carapace forming a continuous bridge behind anal tin ; ventral surface not c.iri- 

 uateel OSTRACIUM, 475. 



476. OSTRACIUM Linnams. 



(Ostracion, Artedi; Linnaeus' Syst. Nat. x, 3:50, 1758: type Ostracion cubicus 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, (darprixiw, diminutive of vffTpdxuv, any hard object, like the 

 shell of a mollusk.) 



. Body three-angled. (Lactophrys Swainson. ) 

 b. No supraocular spine. 



1316. O. trigonuon 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 and 

 ending opposite posterior margin of orbit; carapace open behind the 

 dorsal fin. Head 4 in length; height of sides 2. D. 10; A. 10. West 

 Indies; occasional on our coast southward. 



(Linnaeus, Syst. Nat. x, 330, 1758; Giinther, viii, 256; Goode, Proc. U. S. Nat. Mus. 

 1879, 276: Lactoplirys trigonus Poey, Mem. Hist. Nat. Cuba, ii, 362, 1861.) 



