VEETEBEATA 39 



The orders of which no record is given are known only 

 in the living state. The Plectospondyli represent the 

 highest form of the Malacopterygia, while the Haplomi give 

 the connection with the Acanthopterygia through the Per- 

 cesoces of the latter. Tne Isospondyli offer the connection 

 with the Merospondyli. The Apodal line (the eels), in- 

 cluding orders Nos. 13 to 17, is a degenerate one, ending 

 in the greatly degenerate deep-sea forms of the Lyomeri. 



The orders of the Acanthopterygia are the following : 



A. Scapular arch suspended posterior to the cranium. 



Maxillary bone distinct; no interclav- 

 icles ; epibranchials and pharyngeals 

 present; inferior elements distinct; (1) Opisthomi. 



AA. Scapular arch suspended to cranium by a post- 

 temporal bone. 



a, Ventral fins abdominal. 



Branchial arches developed, third su- 

 perior pharyngeal enlarged; gill- 

 fringes linear ; no interclavicles ; (2) Percesoces. 



Epibranchials and superior pharyngeals 

 reduced in number; gill-fringes 

 linear; interclavicles present; (3) Hemibranchii. 



Epibranchials and superior pharyngeals 



wanting ; gill-fringes in tufts ; (4) Lophobranchii. 



aa, Ventral fins thoracic or jugular. 



j3, Anterior (spinous) dorsal fin expanded 

 into transverse laminse, sessile on cranium. 



Cranium normal; (5) Discocephali. 



^/3, Spinous dorsal fin not transversely ex- 

 panded. 



