20 THE AMERICAN CHARACIDAE. 



few words the marks distinguishing the members of this family from such other fishes with 

 abdominal ventrals and soft rayed fins as the Siluridae, Mormyridae, and Nototeridae. The 

 presence of an adipose dorsal behind the rayed dorsal, although absent in some non-African 

 genera, is a common character of the African fauna which it shares only with the Siluridae, 

 which differ by their naked skin [one of the South American Characins is naked]. The 

 Salmonids which also possess this adipose fin belong, on account of their general structure, to 

 the same great group as the Clupeids which lack it and are strangers to Africa south of the 

 Atlas. 



One of the prime characters used in separating the Characinidae from its nearest related 

 families is the structure of the mouth described as bordered by the premaxillaries in the middle 

 and the maxillaries on the sides, while in the Cyprinidae and Siluridae the upper jaw is said 

 to be bordered by the premaxillaries only. While this definition is valid for the most of the 

 representatives of this family we must not forget, as Segemehl has impressed on us, that 

 there are numerous exceptions which destroy the diagnostic value of this character. Thus the 

 maxillary is so reduced in Serrasalmo, Citharinus, Eugnatichthys, Phago, being confined to 

 the angle of the mouth that it is proper to question if this bone really forms part of the border 

 of the mouth and very recently I have been able to determine that it is absolutely excluded 

 in Ichthyoborus and Neoborus. On the other hand, among Siluridae (Nematognathi), 

 whose premaxillaries are greatly reduced the mouth is bordered laterally by the maxillaries. 

 Chaca has a large maxillary bordering the mouth, Diplomystes and Eutropichthys have a 

 toothed maxillary, and among the Cyprinidae Catostomus shows us the premaxillary and 

 maxillary together forming the mouth border. There are otherwise very great differences in 

 the structure of the jaws among the fishes which are justly united in one family, the Chara- 

 cinidae. Thus the premaxillary, while never protractile, [I have since found Bivibranchia, 

 a new genus, with protractile premaxillaries] is often vertically mobile (like the lower jaw), 

 Ichthyoborinae; the maxillaries are either ankylosed to the premaxillaries or mobile on them, 

 and in the majority of genera they do not directly articulate with the cranium, the only 

 African exception being Sarcodaces. 



The character given by other authors to distinguish the Characins from the Cyprinids, 

 i. e. the non prolongation of the brain capsule between the orbits in the former is not more 

 constant, for in Citharinus and Xenocharax, for example, it extends forward to the nasal 

 region. There are all degrees between this and the more usual one from which the objection- 

 able definition is drawn. The orbitosphenoid, undivided and often membranaceous, forms a 

 large interorbital septum in front of the cerebral cavity or below its anterior part. We have 

 here an important character although it may not be constant, a specialization in this reduc- 

 tion of the anterior part of the basis cranii and in its replacement by a thin interorbital parti- 

 tion. 



The presence of teeth in the jaws does not distinguish the Characins from the Cyprinids 

 because both African and American genera lack them. The teeth vary enormously in struc- 

 ture and furnish valuable characters to distinguish numerous genera of this family. They 

 are found on the premaxillary, the lower jaw, sometimes they are also present on the maxil- 

 laries. They are but rarely found on the palate and none of the African genera offer any 

 examples. 



The branchiostegal rays number only 3 to 5. There are four branchial arches. Pseudo- 

 branchia are lacking or are rudimentary and glandular. The coracoid often forms a ventral 

 ridge. The scapulars, epicoracoid, and postclavicle are distinct. The ventral rays number 

 10 to 13. The first pectoral, the dorsal, and anal rays are but rarely ossified and never form 

 a formidable spine as in the Siluridae. Vertebrae in the African species vary from 17-33 + 

 13-24 = 33-57. 



