The Polycentridæ are small fresh-water perch-like fishes of the streams of South America, without lateral line and with many anal spines.
The Jawfishes: Opisthognathidæ, etc.—The Pseudochromipidæ are marine-fishes of the tropics with the lateral line interrupted, and with a single dorsal. They bear some resemblance to Plesiops and other aberrant Serranidæ.
Fig. 297.—Gnathypops evermanni Jordan & Snyder. Misaki, Japan.
Fig. 298.—Jawfish, Opisthognathus macrognathus Poey. Tortugas, Fla.
Very close to these are the Opisthognathidæ or jawfishes with a single lateral line and the mouth very large. In certain species of Opisthognathus, the maxillary, long and curved, extends far behind the head. The few species are found in warm seas, but always very sparingly. Some of them are handsomely colored.
The Stone-wall Perch: Oplegnathidæ.—A singular group evidently allied to the Hæmulidæ is the family of Oplegnathidæ. In these fishes the teeth are grown together to form a bony beak like the jaw of a turtle. Except for this character, the species are very similar to ordinary grunts. While the mouth resembles that of the parrot-fish, it is structurally different and must have been independently developed. Oplegnathus punctatus, the "stonewall perch" (ishigakidai), is common in Japan, as is also the banded Oplegnathus fasciatus. Other species are found in Australia and Chile.
Fig. 299.—Opisthognathus nigromarginatus. India. (After Day.)