184 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



Neither in Erythrinus nor in the carps do the cranium and surface bones give any 

 reliable suggestions of close relationships with the osteoglossids and mormyrids, which 

 are isospondyls that merely parallel the Ostariophysi in the extension of diverticula of the 



Soc 



UATash. 



Hvdrocyon linealus 



Fic. 69. Ilydrocyon lineatus. Side view. 



swim-bladder into the bony chamber of the inner ear. But in none of these isospondyl 

 families is there any suggestion either of the beginning of a Weberian apparatus or of the 

 development of diverticula which would have the relations with the surrounding parts 

 that obtain in the Ostariophysi. 



The same general type of skull seen in Erythrinus is also shown with minor modifications 

 in the other three characins here figured. The typical characins {Serrasalmo, Hydrocyon) 

 are famous for their ferocity and for the severity of their bites. But although many are 

 predaceous, with sharp teeth, none are of the gulping open-mouthed type; all have relatively 

 short, powerful jaws, typically with close-set, even, sharply cuspidate teeth (Fig. 70), 

 capable of tearing off pieces of the food. The premaxillae are usually strong and well set, 

 the maxillary typically bears teeth, often to the posterior end, but it may become toothless 

 and even be excluded from the mouth (Boulenger, 1910, p. 576). It would seem that the 

 ancestral stock of the characins must have been a form much like Erythrinus, with moder- 

 ately short but strongly attached jaws. 



In Distichodus langi (Fig. 71) the highly specialized mouth is very short antero- 

 posterlorly but wide transversely, bordered by two concentric rows of fine styloid, pointed 

 teeth. The mouth is directed partly downward and there is a peculiar accessory joint 



