. Natural history. Zoology. 492 PISCES—SUB-CLASS lU.—TELEOSTOMI. Of comparatively little importance is the small marine family typified by the genua MoArrnnis. Their chief character is that the body terminates behind in an elongated, tapering, compressed tail, without Family an expanded caudal fin, and is coated with scales, which may Macruridm. be either striated, keeled, or spined. Some of the numerous species measure as much as a yard in length. The last family of the sub-order is that of the flat-fishes, which forms a section to itself, known as the Pleuronectoidei, and characterised by th
. Natural history. Zoology. 492 PISCES—SUB-CLASS lU.—TELEOSTOMI. Of comparatively little importance is the small marine family typified by the genua MoArrnnis. Their chief character is that the body terminates behind in an elongated, tapering, compressed tail, without Family an expanded caudal fin, and is coated with scales, which may Macruridm. be either striated, keeled, or spined. Some of the numerous species measure as much as a yard in length. The last family of the sub-order is that of the flat-fishes, which forms a section to itself, known as the Pleuronectoidei, and characterised by the un- symmetrical conformation of the head and anterior portion Family of the body in the adult. This strange modification renders Pleuronectoidce. the flat-fishes quite distinct from all other members of the class, and by bringing the two eyes to one side of the body— it may be the right or it may be the left—enables them to rest with the other side on the bottom of the sea. Generally, too, they swim in this position, although it is believed that some of the less modified types swim, at least at times, in the normal manner. In this type of fish we have, as Dr. Bashford Dean remarks, " a singular instance of environmental evolution, the flattened body adapting itself both in shape and colour to its bottom-living. Its entire side—not the ventral region, as in the rays—is flattened to the bottom. The unpaired fins now become of especial value ; they increase in size, and their undulatory movements enable the fish to swim rapidly yet retain its one- sided position; ventral fins become useless and degenerate. The further adaptations of the flat-fish include its pigmentation only on the upper or light-exposed side, in this giving one of the most remarkable cases of adapta- tion known among ; Among the rather numerous genera consti- tuting this family, the one in which the adaptation is least developed is Psettodes, represented by a species whose dis
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