=The Sandfishes: Trichodontidæ.=—In the neighborhood of the _Latrididæ_, Dr. Boulenger places the _Trichodontidæ_ or sandfishes, small, scaleless, silvery fishes of the northern Pacific. These are much compressed in body, with very oblique mouths, with fringed lips and, as befits their northern habitat, with a much increased number of vertebræ. They bury themselves in sand under the surf, and the two species, _Trichodon trichodon_ and _Arctoscopus japonicus_, range very widely in the regions washed by the Japan current. These species bear a strong resemblance to the star-gazers (_Uranoscopus_), but this likeness seems to be superficial only. [Illustration: FIG. 302.—Sandfish, _Trichodon trichodon_ (Tilesius). Shumagin Islands, Alaska. ] CHAPTER XXI LABYRINTHICI AND HOLCONOTI =THE Labyrinthine Fishes.=—An offshoot of the _Percomorphi_ is the group of _Labyrinthici_, composed of perch-like fishes which have a very peculiar structure to the pharyngeal bones and respiratory apparatus. This feature is thus described by Dr. Gill: "The upper elements of one of the pairs of gill-bearing arches are peculiarly modified. The elements in question (called branchihyal) of each side, instead of being straight and solid, as in most fishes, are excessively developed and provided with several thin plates or folds, erect from the surface of the bones and the roof of the skull, to which the bones are attached. These plates, by their intersection, form chambers, and are lined with a vascular membrane, which is supplied with large blood-vessels. It was formerly supposed that the chambers referred to had the office of receiving and retaining supplies of water which should trickle down and keep the gills moist; such was supposed to be an adaptation for the sustentation of life out of the water. The experiments of Surgeon Day, however, throw doubt upon this alleged function, and tend to show: (1) that these fishes died when deprived of access to atmospheric air, not from any deleterious properties either in the water or in the apparatus used, but from being unable to subsist on air obtained solely from the water, aerial respiration being indispensable; (2) that they can live in moisture out of the water for lengthened periods, and for a short, but variable period in water only; and (3) that the cavity or receptacle does not contain water, but has a moist secreting surface, in which air is retained for the purpose of respiration. It seems probable that the air, after having been supplied for aerial respiration, is ejected by the mouth, and not swallowed to be discharged per anum. In fine, the two respiratory factors of the branchial apparatus have independent functions: (1) the labyrinthiform, or branchihyal portion, being a special modification for the respiration of atmospheric air, and (2) the gill filaments discharging their normal function. If, however, the fish is kept in water and prevented from