18 THE AMERICAN CHARACIDAE. 



ossicles for placing the air-bladder in communication with the auditory appa- 

 ratus. The first four vertebrae are modified. The first vertebra lacks the 

 superior arch which is replaced by the "claustrum" and "scaphium" of the 

 Weberian apparatus; the principal ossicle of the series, the "tripus," is associated 

 with the third vertebra consisting of the rib and parapophysis of the third 

 vertebra. The " inter calarium," representing the neural arch of the second 

 vertebra, is imbedded in the ligament extending from the tripus to the scaphium. 

 Very frequently the air-bladder comes in close contact with the skin, forming 

 a pseudotympanum above the pectorals. In the Characins the area is not 

 unfrequently marked by a humeral spot, a gathering of pigment cells from 

 contiguous areas. This spot may become shifted away from the tympanum. 

 The air-bladder is usually connected with the intestine by a duct. The pectoral 

 girdle is suspended from the skull by a long posttemporal; the mesocoracoid 

 is present and the ventral fins are abdominal. 



The orders and suborders of the Ostariophysi may be separated by the 

 following key: — 



a. Maxillary bone usually a toothless vestige carrying a barbel; no subopercle or sympleetic; no 

 scales; supraoccipital and parietals coossified; mouth usually with teeth; ribs attached to trans- 

 verse apophyses; skin naked or covered with bony plates. Usually an adipose dorsal. 



Nematognathi or Siluroidea. 

 aa. Maxillary usually well developed, not forming the base of a barbel, but sometimes one or more small 

 barbels at or near its end; subopercle and syrnplectie present; parietals distinct from the supra- 

 occipital; thoracic vertebrae without parapophyses; ribs mostly sessile; naked or with scales. 



Plectospondyli or Cyprinoidea. 



b. Lower pharyngeals falciform, parallel with the gill-arches; jaws toothless; brain-case produced 



between the orbits; basis cranii simple; two superior pharyngeals; mouth without teeth, more 



or less protractile; no adipose fin (Eventognathi or Cyprinipormes). 



66. Lower pharyngeals not falciform; three basal branchihyals; basis cranii double, sometimes 

 with myodome; one to four superior pharyngeals; mouth usually not protractile, usually with 

 teeth. 

 f. Anus submedian; body variously shaped, never eel-shaped; dorsal and usually an adipose fin 



present; ventrals abdominal (Heterogxathi or Characiformes). 



cc. Anus at throat; body eel-shaped; dorsal absent, or reduced; ventrals absent.. . (Gymxoxoti). 



The Eventognathi do not enter the Neotropical realm. The Gymnonoti 

 are confined to it, the Heterognathi, as stated, occur in Africa and South America. 

 The Nematognathi have an all but universal distribution. 



Sagemehl (Morphologische jahrbuch, 1884, 10) pointed out the similarity 

 of the Erythrinoids to Amia, and suggested the derivation of the family from the 

 Holostei and more particularly from the Cycloganoidea. Boulenger (Poisson 

 bassin Congo, 1901) considers the Characidae, more particularly the Erythrins, 



