_Malacosteus niger_, Ayres (Plate XXII.), is a rare fish, from a depth of two-thirds of a mile; though several specimens have recently been taken by the United-States Fish-Commission, and others by the “Talisman” off Morocco, in forty-eight hundred feet of water. It is of small size, from thirteen to fourteen centimeters in length, of a velvet-black hue, and possesses two large luminous organs upon the head; one of which, according to M. Filhol, who observed the light in the living fish, emits a golden, and the other a greenish phosphorescence. We have here, then, a fish that vies with the _Appendicularia_, and other forms which we have seen emitting light of more than one color. It is possible that the rays of light from these spots project ahead of the fish, in the manner shown in the accompanying figure, in which the appearance of the light is of course conjectural; but as to the meaning of the different colors, are they a system of signals cunningly devised by Nature to enable _Malacosteus_ to distinguish its kind in the profound depths of the ocean, or are they merely lures of more than ordinary brilliancy? In some fishes the luminous organs are extremely small, almost invisible to the naked eye, and often spread over a large extent of surface. Such an instance is seen in _Eustomias obscurus_ (Plate XIX.) and _Neostoma_. In the former, an attenuated carnivorous fish of a jet-black color, we see another example of remarkable feelers, or sense-organs. While these forms are probably free swimmers, there are many others that are mud-dwellers, of most extraordinary make-up, literally living bags, or rather mouths. The _Melanocetus Johnstoni_ (Günther, Plate XXIII.) is one of these; having an enormous pouch, with a fishing-rod upon its head similar to that of our common _Lophius_. _Melanocetus_ probably buries itself in the ooze, as shown in the engraving, allowing the tip of its tentacle, or rod, to protrude; and, when the living bait is touched, it opens its cavernous mouth and seizes the victim.