32 PISCES. — GANOIDEI. 



BB. Dorsal fins two, the anterior spinous; teeth incisor-like. 



Balistid.e. 90. 

 BBD. Dorsal fin single, of soft rays only. 

 E, Snout tubular, bearing the short toothless jaws at the end; body 



mailed Syngxathid-e, 43. 



EE. Snout not tubular. 



F. Body elongate, eel-shaped : mamillaries 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. 



ANGTrn.tiiD.fi, 40. 

 GG. Lower jaw not projecting; skin scaleless. . . Echelid.e, 41. 

 FF. Body not eel-shaped. 

 II. Breast with a sucking-disk. 



I. Skin smooth Lipariduxe, 77. 



//. Skin warty Cyclopterid^e, 78. 



////. Breast without sucking di>k. 

 J. Teeth in each jaw confluent into one. 



A'. Body compressed, the skin rough Molid.e, 93. 



A' A'. Body not compressed, armed with spines. 



Diodontid.e, 92. 

 J J. Teeth in sach jaw confluent into two. Tetraodontid.e, 91. 

 .4.1. Gill membranes free from the isthmus. 



L. Vent at the throat; vertical fins separate. . . Amblyopsidje, 36. 

 LL. Vent normal. 



M. Caudal fin wanting; body naked Trichicrid.e, 54. 



MM. Caudal fin present 



N. Upper jaw produced in a sword Xiphiid.e, 52. 



NX. Upper jaw without sword. 



0. Body ovate, much compressed Stromateid^e, 58. 



00. Body oblong or elongate; gill membranes not united. 

 P. Jaws toothless, the lower projecting . Ammodytidjs, 49. 

 PP. Jaws with teeth, the lower not projecting. Ophidiid.e, 87. 



Series GAXOIDEI. (The Gaxoid Fishes.) 



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 zoologists, 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- 



