Five species. The males are most beautifully coloured, and their dorsal fin is much enlarged. In one species (M. hellerii), besides, the lower caudal rays of the mature male are prolonged into a long, sword-shaped, generally black and yellow appendage.
Two other genera belong to this group: Platypoecilus and Girardinus.
Seventh Family—Heteropygii.
Head naked; body covered with very small scales; barbels none. Margin of the upper jaw formed, by the intermaxillaries. Villiform teeth in the jaws and on the palate. Adipose fin none. Dorsal fin belonging to the caudal portion of the vertebral column, opposite to the anal. Ventral fins rudimentary or absent. Vent situated before the pectorals. Stomach coecal; pyloric appendages present. Pseudobranchiæ none; air-bladder deeply notched anteriorly.
To this small family, which is closely allied to the Cyprinodonts and Umbridæ, belongs the famous Blind Fish of the Mammoth Cave in Kentucky, Amblyopsis spelæus. It is destitute of external eyes, and the body is colourless; although the eyes, with the optic nerve, are quite rudimentary, the optic lobes are as much developed as in fishes with perfect eyes. The loss of vision is compensated by the acuteness of its sense of hearing, as well as by a great number of tactile papillæ, arranged on transverse ridges on the head, and provided with nervous filaments coming from the fifth pair. The ovary is single, and the fish is viviparous, like the Cyprinodonts. It seems to occur in all the subterranean rivers that flow through the great limestone region underlying the carboniferous rocks in the central portion of the United States. As in Cyprinodon, so in this genus, specimens occur without ventral fins; they have been called Typhlichthys. The largest size to which Amblyopsis grows is five inches.
Chologaster is closely allied, but provided with small external eyes; its body is coloured, but it is destitute of ventrals. It was found once in a rice field in South Carolina.
[See Tellkampf, Müll. Arch. 1844, p. 381; Packard and Putnam, “The Mammoth Cave and its Inhabitants.” Salem. 1872. 8o.]
Eighth Family—Umbridæ.
Head and body covered with scales; barbels none. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally. Adipose fin none; the dorsal fin belongs partly to the abdominal portion of the vertebral column. Stomach siphonal; pyloric appendages none; pseudobranchiæ glandular, hidden; air-bladder simple.
Two small species only are known: Umbra krameri from Austria and Hungary, and Umbra limi, locally distributed in the United States; called “Hunds-fish” in Germany, “Dog-fish” or “Mud-fish” in America.