SYSTEMATIC RELATIONS OF FISHES. 589 
Anterior vertebre,. similar, distinct, without ossicula auditus. 
8. Isospondyli— Herring, ete. 
No preecoracoid arch. 
A. Scapular arch suspended to cranium. 
A symplectic. 
Pterotic and anterior vertebra meee parietal separated by 
supra-occipital. 9. Haplomi— Pike, e 
Anterior vertebrae modified ; cil. ed: pectoral fins. 10. 
Glanencheli — Electric eel. 
B B. No symplectic. 
Anterior vertebrz simple; a preeoperculum and maxillary ; no 
pectoral fins. 11. Ichthyocephali—Java eels. 
A Scapular arch free behind the cranium. 
* A. Preoperculum. 
A symplectic ; maxillary well deveirant: no pectoral fins. 12. 
Holostomi— Symbranchi. 
No symplectic; maxillary lost on connate; pectoral fins. 13. 
Taepa — Eels proper. 
* Preoperculum wanting or rudimental. 
No symplectic, maxillary, nor pectoral fins, no pterygoid. 14. 
Colocephali — Murænæ. 
the above orders the Haplomi (pike, etc.) approach nearest 
the Physoclysti of the families Opheocephalide and Atherinide ; 
and the Holostomi of the family Symbranchide, to the Physoclyst 
family of Mastacembelide. The affinities between these families 
is in both cases so close as to render the distinction of the prima- 
ry divisions in question hardly worth preserving. 
The complete development of the support of the caudal fin 
is seen in many members of this tribe, while in others it re- 
mains in its primitive condition. Among Physoclysti it is nearly 
always complete, though in a few ( Trichiuride), etc., it remains 
larval. In the first development of the vertebral column in fishes, 
it forms a straight axis. The fin is represented by a fold of the 
integument which extends equally round its extremity. In this 
membrane the rays are developed, and in many fishes they remain 
thus equally distributed. In this case the caudal vertebrae remain 
in a straight line to the extremity, and we have a termination such 
as is seen in Lepidosiren and the eels. This form of tail may be 
called the isocercal. 
If now the radii basal or distal, acquire a greater development 
