212 



ZOOLOGY 



SECT. 



The only existing members of this order are several species of 





FIG. 883. Folypterus bichir. A, entire animal ; B, 

 ventral view of throat, an. anus ; br. m. branchiostegal 

 membrane ; c. f. caudal fin ; d. f. dorsal finlets ; jug. pi. 

 jugular plates ; na. nostril ; pet. f. pectoral fin ; pv. f. 

 pelvic fin ; v. f. ventral fin. (After Cuvier.) 



Polypterus (Fig. 883) from the Congo and Upper Nile, and Cala- 

 moichthys calabaricus from Old Calabar. 



ORDER 2. CHONDROSTEI. 



Teleostomi in which the paired fins have no basal lobe, but their 

 whole free portion is supported by dermal rays. There are few 

 replacing bones in the skull, and the primary shoulder-girdle is 

 unossified. The vertebral column is represented by a persistent 

 notochord with cartilaginous arches, and its anterior end is fused 

 with the cranium. Branchiostegal rays are few or absent. The tail 



pclj 



FIG. 884. Acipenser ruthenus (Sturgeon), b. barbels ; c./. caudal fin ; d. /. dorsal fin; 

 pet. /. pectoral fin ; pv. /. pelvic fin ; sc. scutes ; v. /. ventral fin. (After Ouvier.) 



is heterocercal. The pelvic fins are abdominal. A spiral valve, 

 conus arteriosus, and optic chiasma are present. 



This order includes the Sturgeons (Acipenser, Fig. 884, and 

 Scaphirhynchus) found in the rivers of Europe, Asia, and North 

 America ; the curious spoon-billed Polyodon, from the Mississippi ; 

 and Psephurus from the rivers of China. 



ORDER 3. HOLOSTEI. 



Teleostomi in which the paired fins have no basal lobe. The 

 chondrocranium is well ossified by replacing bones and investing 

 bones : branchiostegal rays are present. The vertebral column 

 consists of bony vertebrae, and the tail is heterocercal or nearly 



