32 PISCES, — GANOIDEL. 
BB. Dorsal fins two, the anterior spinous; teeth incisor-like. 
BALIsTID#, 90. 
BBB. Dorsal fin single, of soft rays only. 
£, Snout eeu bearing the short toothless jaws at the end; body 
mailed. 2 te e % «6 «© «© « SYNGNATHIDA, 43. 
EE. Snout ‘tol tubular. 
F. Body elongate, eel-shaped; maxillaries and premaxillaries coales- 
cent with vomer and palatines. 
G. Lower jaw projecting ; skin covered with linear imbedded 
scales arranged at right angles with each other. 
ANGUILLIDA, 40. 
GG. Lower jaw not projecting; skin scaleless.. . Ecuunip.1, 41. 
FF. Body not eel-shaped. 
4. Breast with a ee 
J. Skin smooth. . . . 2 oe e «© © | ©) 6©LIpARpips, 77. 
JI, Skin warty... . . + + » CYCLOPTERIDA, 78. 
HH. Breast without eudiion disk. 
J. Teeth in each jaw confluent into one. 
K. Body compressed, the skin rough. . . . . Mowips, 93, 
KK. Body not compressed, armed with spines. 
Diopoytip#, 92. 
JJ. Teeth in each jaw confluent into two. TETRAODONTID*, 91. 
AA, Gill membranes free from the isthmus. 
L. Vent'at the throat; vertical fins separate. . . AMBLYOPSIDA, 36. 
LL. Vent normal. 
M. Caudal fin wanting; body naked.. . . . . TricmruRipa, 54. 
MM. Caudal fin present. 
N. Upper jaw produced inasword.. . . . . + XIPHIIDA, 52. 
NN. Upper jaw without sword. 
0. Body ovate, much compressed... . . . STROMATEID#, 58. 
00. Body oblong or elongate; gill membranes not united. 
P. Jaws toothless, the lower projecting . AMMODYTID&, 49, 
PP. Jaws with teeth, the lower not projecting. Opnipims, 87. 
Serirs GANOIDEI. (Tue Ganon Fisues.) 
The name Ganoidei was first used by Agassiz for those fishes 
which are armed with bony plates, instead of regular cycloid or 
ctenoid scales. Later, Johannes Miiller, one of the greatest of 
systematic zodlogists, restricted the group to those fishes which 
show more or less distinct reptilian or batrachian affinities, and 
especially affinities with the mailed fishes of the Devonian and 
Carboniferous ages. The group is a heterogeneous one, and one 
practically scarcely susceptible of definition. Some of the Ganoids 
are closely allied to the Teleosts; some approach the Dipnoi, and 
some again resemble the Holocephali. The existence of the solid 
optic chiasma, the presence of several valves in the arterial bulb, 
and of a more or less developed spiral valve in the rectum, distin- 
