FIG. 164.—Alaska Blackfish, _Dallia pectoralis_ (Bean). St. Michaels, Alaska. ] "In the deep-sea eels of the order _Heteromi_ there is a somewhat similar condition of the coracoid elements inasmuch as the hypercoracoid and hypocoracoid though present are merely membranous elements surrounded by cartilage and the actinosts are greatly reduced. It seems probable that we are dealing in the two cases with independent degeneration of the shoulder-girdle and that the two groups (_Xenomi_ and _Heteromi_) are not really related." (Gilbert.) Of the single family _Dalliidæ_, one species is known, the Alaska blackfish, _Dallia pectoralis_. This animal, formed like a mud-minnow, reaches a length of eight inches and swarms in the bogs and sphagnum swamps of northwestern Alaska and westward through Siberia. It is found in countless numbers according to its discoverer, Mr. L. M. Turner, "wherever there is water enough to wet the skin of a fish," and wherever it occurs it forms the chief food of the natives. Its vitality is most extraordinary. Blackfishes will remain frozen in baskets for weeks and when thawed out are as lively as ever. Turner gives an account of a frozen individual swallowed by a dog which escaped in safety after being thawed out by the heat of the dog's stomach. CHAPTER XI ACANTHOPTERYGII; SYNENTOGNATHI =ORDER Acanthopterygii, the Spiny-rayed Fishes.=—The most of the remaining bony fishes constitute a natural group for which the name _Acanthopterygii_ (ἄκανθα, spine; πτερύξ, πτερόν, fin or wing) may be used. This name is often written _Actinopteri_, a form equally correct and more euphonious and convenient. These fishes are characterized, with numerous exceptions, by the presence of fin spines, by the connection of the ventral fins with the shoulder-girdle, by the presence in general of more than one spine in the anterior part of dorsal and anal fins, and as a rule of one spine and five rays in the ventral fins, and by the absence in the adult of a duct to the air-bladder. Minor characters are these: the pectoral fins are inserted high on the shoulder-girdle, the scales are often ctenoid, and the edge of the upper jaw is formed by the premaxillary alone, the maxillary being always toothless.