3 2 ° 



BEL ONORH YNCHIDA E 



Scaphirhynchus, Heckel (Fig. 300) ; rivers of N. America and Central 



Asia. 



Acipenser rutkenns, 1.. : the Sterlet. (After Cuvier.) 1, rostrum ; -2, mouth ; 3, pectoral, 

 I. pelvic, '>. anal. 6, caudal, and 7. dorsal (in ; 8, dorsal bony scute; 0, nostrils. 



Incertae sedis. 



Family Beloxorhynchidae. An extinct family of fish from 

 Triassic and Liassic deposits, which have been placed sometimes with 

 the 'Ganoids' (Heckel [205«]), at other times with the Teleostei (Pictet, 

 Liitken, Zittel [512]). They have been placed by A. S. Woodward 

 [505] among the Chondrostei ; but their real position seems so uncer- 

 tain, that it is better not to include them in that sub-order for the 

 present. The presence of clavicles and the possession in the median 

 fins of lepidotrichia which are more numerous than the supporting 

 radiate, the most important characters they have in common with the 

 Chondrostei, are after all but signs of primitiveness ; which evidence is, 

 moreover, somewhat invalidated by the fact that the radials resemble 

 rather those of higher Actinopterygii in being mainly composed of a 



Fig. 3oo. 

 Scaphirhynchus platorhynclius, Hat. (From Jordan and Evermann.) 



long proximal segment. The symmetrical caudal fin is apparently of 

 the abbreviate diphycercal type, quite unlike that of any Chondrostean 

 or primitive Ilolostean, and suggesting affinity with the Osteolepidoti. 

 The dermal bones of the skull form a continuous shield in the adult, 

 extending far back over the occiput, over the sides of the head, round 

 the orbit, and forwards projecting into a greatly elongated pointed snout 

 (Fig. 301). The lower jaw is similarly drawn out ; it is very deep 

 behind. The dentition consists of large and small conical teeth. There 

 appear to be no median or lateral gulars, and only one large opercular. 



