Three species of small size from various parts of South America; the species figured is represented of the natural size, and comes from the Upper Amazons.
Megalobrycon.—Dorsal fin placed in middle of the length of the body, immediately behind the ventrals. Anal long. Abdomen rounded in front of, and somewhat compressed behind, the ventrals. Cleft of the mouth of moderate width. Teeth notched, in a triple series in the intermaxillary, and in a single in the maxillary and mandible; no other teeth behind the mandibulary teeth or on the palate. Scales of moderate size, with the free portion striated.
One species from the Upper Amazons (M. cephalus). Specimens more than one foot long have been obtained.
Fig. 278.—Megalobrycon cephalus.
Gastropelecus.—Dorsal fin placed behind the middle of the length of the body, above the anal; anal long; pectoral long; ventrals very small or rudimentary. Body strongly compressed, with the thoracic region dilated into a sub-semicircular disk. Scales of moderate size. Lateral line descending obliquely backwards towards the origin of the anal fin. The lower profile compressed into an acute ridge. Cleft of the mouth of moderate width; teeth compressed, tricuspid, in one or two series in the intermaxillary, and in a single in the mandible; maxillary with a few minute conical teeth; palate toothless.
Three specimens of this singular form are known from Brazil and the Guyanas; they are of very small size.
The majority of the other genera belonging to this group are South American, viz. Piabucina, Scissor, Pseudochalceus, Aphyocharax, Chalceus, Brycon, Chalcinopsis, Bryconops, Creagrutus, Chalcinus, Piabuca, Paragoniates, and Agoniates; two only are African, viz. Nannæthiops, which represents the South American Tetragonopterus, and Bryconæthiops, which is allied to Brycon.
VII. Hydrocyonina.—A short dorsal and an adipose fin; teeth in both jaws well developed and conical; gill membranes free from the isthmus; nasal openings close together. South America and Tropical Africa. Fishes of prey.
Hydrocyon.—The dorsal fin is in the middle of the length of the body, above the ventrals; anal of moderate length. Body oblong, compressed, covered with scales of moderate size; belly rounded. Cleft of the mouth wide, without lips; the intermaxillaries and mandibles are armed with strong pointed teeth, widely set and few in number; they are received in notches of the opposite jaw, and visible externally when the mouth is closed. Palate toothless. Cheeks covered with the enlarged sub-orbital bones. Orbit with an anterior and posterior adipose eyelid. Intestinal tract short.