FISHES. 201 



SUB-CLASS II. Tail heterocercal ; optic nerves forming a chiasma ; 

 arterial bulb with several rows of valves ; air bladder fre- 

 quently cellular and lung-like ; exoskeleton typically of bony 

 plates GANOIDEI, page 212. 



ORDERS OF TELEOSTEI. 

 Gills pectinated of the ordinary sort, not tuft-like. 



I. Maxillaries normally developed and normally distinct from 

 each other; gills not in the axils; typical fishes (characters 

 too various to be here summarized). . TELEOCEPHALI, Z. 



II. With 4 to 8 long barbels about the mouth, the longest of 



which is a continuation of the incomplete maxillary; 

 subopercle wanting ; ventrals abdominal ; usually an adi- 

 pose fin and dorsal and pectoral spines; skin naked or 

 with bony plates ; chiefly in fresh water. 



NEMATOGNATHI, AA. 



III. Maxillaries rudimentary or wanting; scapular arch free 

 from skull; body elongated, serpentiform, with a long 

 dorsal and anal, which meet around the tail ; no ventral 

 fins; scales small or none; jaws with teeth; chiefly 

 marine ABODES, BB. 



IV. Carpal bones elongated, forming a kind of arm which sup- 



ports the pectorals, in the axils of which are the small gill 

 openings ; ventrals j ugular, with 4 or 5 soft rays ; body 

 scaleless or tuberculate ; head very large ; marine. 



PEDICULATI, page 211. 



V. Intermaxillaries immovably united with the maxillaries ; 



skin rough, often covered with spines or ganoid plates ; 



ventral fins wanting; marine. PLECTOGNATHI, page 212. 



** Gills small, tuft-like, largest at their free tips ; body covered 



with bony plates ; mouth small, toothless, at the end of the 



long snout; no ventral fins; marine. 



LOPHOBRANCHII, page 212. 



Z. SUB -ORDERS OF TELEOCEPHALI. 



I. Body flat, unsymmetrical ; both eyes on the upper or colored 



side; ventrals jugular. . . HETEKOSOMATA, page 208. 



II. Bones of snout prolonged into a long tube which bears the 



short jaws at the end. . . HEMIBRANCHII, page 209. 



