Thus _Balistes_, the trigger-fish, has 17 vertebræ; _Monacanthus_ and _Alutera_, foolfishes, about 20; the trunkfish, _Ostracion_, 14; the puffers, _Tetraodon_ and _Spheroides_, 18; _Canthigaster_, 17; and the headfish, _Mola_, 17. Among the _Pediculates, Malthe_ and _Antennarius_ have 17 to 19 vertebræ, while in their near relatives, the anglers, _Lophiidæ_, the number varies with the latitude. Thus, in the northern angler, _Lophius piscatorius_, which is never found south of Cape Hatteras, there are 30 vertebræ. In a similar species, inhabiting the north of Japan (_Lophius litulon_), there are 27. In another Japanese species, ranging farther south, _Lophiomus setigerus_, the vertebræ are but 19. Yet in external appearance these two fishes are almost identical. It is, however, a notable fact that some of the deep-water _Pediculates_, or angling fishes, have the body very short and the number of vertebræ correspondingly reduced. _Dibranchus atlanticus_, from a depth of 3600 fathoms, or more than 4 miles, has but 18 vertebræ, and others of its relatives in deep waters show also small numbers. These soft-bodied fishes are simply animated mouths, with a feeble osseous structure, and they are perhaps recent offshoots from some stock which has extended its range from muddy bottom or from floating seaweed to the depths of the sea. A very few spiny-rayed families are wholly confined to the northern seas. One of the most notable of these is the family of viviparous surf-fishes (_Embiotocidæ_), of which numerous species abound on the coasts of California and Japan, but which enter neither the waters of the frigid nor of the torrid zone. The surf-fishes have from 32 to 42 vertebræ, numbers which are never found among tropical fishes of similar appearance or relationship. The facts of variation with latitude were first noticed among the _Labridæ_. In the northern genera (_Labrus_, _Tautoga_, etc.) there are 38 to 41 vertebræ; in the semi-tropical genera (_Crenilabrus_, _Bodianus_, etc.), 30 to 33; in the tropical genera (_Halichoeres_, _Xyrichthys_, _Thalassoma_, etc.), usually 24. Equally striking are the facts in the great group of _Pareioplitæ_, or mailed-cheek fishes, composed of numerous families, diverging from each other in various respects, but agreeing in certain peculiarities of the skeleton. Among these fishes the family most nearly related to ordinary fishes is that of the _Scorpænidæ_ (scorpion-fishes, etc.). This is a large family containing many species, fishes of local habits, swarming about the rocks at moderate depths in all zones. The species of the tropical genera have all 24 vertebræ. Those genera chiefly found in cooler waters, as in California, Japan, Chile, and the Cape of Good Hope, have in all their species 27 vertebræ, while in the arctic genera there are 31.