Allied to the _Scorpænidæ_, but confined to the tropical or semi-tropical seas, are the _Platycephalidæ_, with 27 vertebræ, and the _Cephalacanthidæ_ (flying gurnards), with but 22. In the deeper waters of the tropics are the _Peristediidæ_, with 33 vertebræ, and extending farther north, belonging as much to the temperate as to the torrid zone, is the large family of the _Triglidæ_ (gurnards) in which the vertebræ range from 25 to 38. The family of _Agonidæ_ (sea-poachers), with 36 to 40 vertebræ, is still more decidedly northern in its distribution. Wholly confined to northern waters is the great family of the _Cottidæ_ (sculpins), in which the vertebræ ascend from 30 to 50. Entirely polar and often in deep waters are the _Liparididæ_ (sea-snails), an offshoot from the _Cottidæ_, with soft, limp bodies, and the vertebræ 35 to 65. In these northern forms there are no scales, the spines in the fins have practically disappeared, and only the anatomy shows that they belong to the group of spiny-rayed fishes. In the _Cyclopteridæ_ (lumpfishes), likewise largely arctic, the body becomes short and thick, the back-bone inflexible, and the vertebræ are again reduced to 28. In most cases, as the number of vertebræ increases, the body becomes proportionally elongate. As a result of this, the fishes of arctic waters are, for the most part, long and slender, and not a few of them approach the form of eels. In the tropics, however, while elongate fishes are common enough, most of them (always excepting the eels) have the normal number of vertebræ, the greater length being due to the elongation of their individual vertebræ and not to their increase in number. Thus the very slender goby, _Gobionellus oceanicus_, has the same number (25) of vertebræ as its thick-set relative _Gobius soporator_ or the chubby _Lophogobius cyprinoides_. In the great group of blenny-like fishes the facts are equally striking. The arctic species are very slender in form as compared with the tropical blennies, and this fact, caused by a great increase in the number of their vertebræ, has led to the separation of the group into several families. The tropical forms composing the family of _Blenniidæ_ have from 28 to 49 vertebræ, while in the arctic genera the numbers range from 75 to 100. Of the true _Blennidæ_, which are all tropical or semi-tropical, _Blennius_ has 28 to 35 vertebræ; _Salarias_, 35 to 38; Lepisoma, 34; _Clinus_, 49; _Cristiceps_, 40. A fresh-water species of _Cristiceps_ found in Australia has 46. Blennioid fishes in the arctic seas are _Anarrhichas_, with 76 vertebræ; _Anarrhichthys_, with 100 or more; _Lumpenus_, 79; _Pholis_, 85; _Lycodes_, 112; _Gymnelis_, 93. _Lycodes_ and _Gymnelis_ have lost all the dorsal spines.