Isospondyli 39 



ventral fins are abdominal, that is, inserted backward, so that 

 the pelvis is free from the clavicle, the two sets of limbs being 

 attached to different parts of the skeleton. Most of the ab- 

 dominal fishes are also soft-rayed fishes, that is, without con- 

 secutive spines in the dorsal and anal fins, and they show a number 

 of other archaic peculiarities. The Malacopterygians (j*a\a/c6s, 

 soft; Trrepvt;, fin) of Cuvier therefore correspond very nearly 

 to the Abdominales. But they are not quite the same, as the 

 spiny-rayed barracudas and mullets have abdominal ventrals, 

 and many unquestioned thoracic or jugular fishes, as the sea- 

 snails and brotulids, have lost, through degeneration, all of their 

 fin-spines. 



In nearly but not quite all of the Abdominal fishes the 

 slender tube connecting the air-bladder with the oesophagus 

 persists through life. This character defines Muller's order 

 of Physostomi ((pvcrds, bladder; o-ro^a, mouth), as opposed to 

 his Physoclysti (0v<ros, bladder; /c-Aezcrrds, closed), in which this 

 tube is present in the embryo or larva only. Thus the Thoracices 

 and Jugulares, or fishes having the ventrals thoracic or jugular, 

 together correspond almost exactly to the Acanthopterygians, 

 (ctKavda, spine ; nrepvg, fin), or spiny-rayed fishes of Cuvier, or to 

 the Physoclysti of Muller. The Malacopterygians, the Abdomi- 

 nales, and the Physostomi are in the same way practically 

 identical groups. As the spiny- rayed fishes have mostly ctenoid 

 scales, and the soft-rayed fishes cycloid scales, the Physostomi 

 correspond roughly to Agassiz's Cycloidei, and the Physoclysti 

 to his Ctenoidei. 



But in none of these cases is the correspondence perfectly 

 exact, and in any system of classification we must choose charac- 

 ters for primary divisions so ancient and therefore so perma- 

 nent as to leave no room for exceptions. The extraordinary 

 difficulty of doing this, with the presence of most puzzling 

 intergradations, has led Dr. Gill to suggest that the great body 

 of bony fishes, soft-rayed and spiny-rayed, abdominal, thoracic, 

 and jugular alike, be placed in a single great order which he 

 calls Teleocephali (reAeoV, perfect; Ke^aXrf, head). The aberrant 

 forms with defective skull and membrane-bones he would sepa- 

 rate as minor offshoots from this great mass with the name 

 of separate orders. But while the divisions of Teleocephali 



