182 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



and Cypriniformes. In the Cyprinidse the lapillus may be remarkably different in form in 

 closely related species in which the lagenar otoliths are closely similar or almost indis- 

 tinguishable. The sagitta, which in most orders affords diagnostic characters, in this sub- 

 order is small and attenuated. 



The number of branchiostegal rays, according to Hubbs (I9I9, p. 65), varies widely 

 in the Ostariophysi. In cyprinids it is never more than three, in characins from three to 

 five, in the Nematognathi, six, seven, nine, eleven. The low number of branchiostegals 

 in certain malacopterygian fishes is usually correlated with the broad union of the branchial 

 membranes and with a freshwater habitat (Hubbs). 



Heterognathi (Characins) 



One of the least specialized skulls in the entire order is possessed by the characin 

 Erythrinus (Fig. 67) of the primitive family Erythrininse. Indeed in this connection 

 Sagemehl (1885, p. 117) came to the following important conclusion: 



soc P*"^ .supcl 



scale bone 



pf I, pareth 

 deth 



Erythrinua unitaeniatus 



Fig. 67. Erythrinus unitcrniatus . Side view. 



"Wie es sich klar ergiebt, lassen sich die Characiniden in den meisten Organisations- 

 verhaltnissen direkt an die bei Amia bestehenden anschliessen, und zwar ist es die Gruppe 

 der Erythrininen, welche die grosste Uebereinstimmung erkennen lasst. Nur in wenigen 

 Punkten ist ein Anschluss nicht moglich und miissen wir in diesen Fallen auf tiefer stehende 

 Formen als Amia zuriickgehen. Jedenfalls stand die Stammform der Characiniden nicht 

 fern von Amia." 



It seems more probable, however, that at least part of this resemblance is convergent, 



