266 Isospondyli 
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 (uadaxos, 
soft; arepvé, 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 cesophagus 
persists through life. This character defines Muller’s order 
of Physostomi (g@vods, bladder; oréua, mouth), as opposed to 
his Physoclysti (@voos, bladder; «Aeiords, 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, 
(axavéa, spine; zrepvé, fin), or spiny-rayed fishes of Cuvier, or to 
the Physoclystt of Muller. The Malacopterygians, the Abdomz- 
nales, and the Physostomt 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 Cycloidet, and the Physoclysti 
to his Ctenoider. 
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 Teleocephalt (reAeos, perfect; ce@adn, 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 
