ACANTHOPTERYGII 



671 



present ; palate toothless ; lower pharyngeal bones more or less 

 completely united, with median suture. Vertebrae with para- 

 pophyses from the third ; ribs most frequently sessile or subsessile. 

 A single nostril on each side. Gill-membranes free from isthmus ; 

 5 or 6 branchiostegal rays ; gills 4, a slit behind the fourth ; 

 pseudobranchiae absent. Dorsal fin, with numerous spines ; anal 

 with 3 spines or more. Ventral fins with 1 spine and 5 soft rays. 

 Fresh or brackish-water fishes, variable in form and dentition, 

 some carnivorous, others chiefly herbivorous. In some American 

 forms (Ciclilci} the males and females differ during the spawning 

 season, the male developing a hump on the top of the head, which 



FIG. <ilO. Tilapia dardennii, from Lake Tanganyika. ^ nat. size. 



disappears afterwards. The eggs and young are cared for by the 

 parents ; either the male or the female, according to the species, 

 sheltering them in the mouth or pharynx. 1 These fishes, often 

 designated as " Chromides," a name which properly pertains to 

 members of the following family, inhabit Africa, Madagascar, 

 Syria, India and Ceylon, and Central and South America, from 

 Texas to Uruguay. About 45 genera are distinguished, based 

 mostly on the number of anal spines and the dentition, which for 

 variety of types is comparable to that of the Characinidae. Of 

 these 45 genera, 30 are African. 150 species are known from 

 Africa (with Syria and Madagascar), 140 from America, and 3 

 from India and Ceylon. 2 Principal genera African : Lampro- 

 logus, Hemichromis, Paratilapia, Xenotilapia, Tropheus, Tilapia, 



1 It has recently been ascertained, on a large number of specimens, that in the 

 African species the female alone performs the buccal nursing duties. 



2 Cf. Monograph by J. Pellegrin (Paris, 1904). 



