14. The Evolution of the Catfishes. [ ZOE 
From the primitive Ageneiosine and Auchenipterine have evi- 
dently been derived, as a lateral offshoot, the Pygidide, of which the 
Cetopsine retain the most ancestral traits. In this family nasal bar- 
bels again appear. Some members of Stegophelinz have lost the 
habit of free swimming, and live as commensals in the gill cavity of 
large species of Siluridz. 
The three remaining families were, by Dr. Giinther, united in one 
of his inferior groups, Hypostomatina. They have little external 
resemblance to the Siluride. 
The Callichthyide have two series of smooth plates covering the 
sides, while the Loricariida have several series of rough plates. 
_ The teeth and dentiferous bones of the latter have also been consid- 
erably modified. The Argiidee are dwarfed forms inhabiting high 
mountain streams. 
As diagnoses of the families enumerated here were published by 
us*, and more detailed descriptions of both the families and sub- 
families will appear in a subsequent paper already referred to, no 
further descriptions will be necessary here. We wish to raise the 
genus Diplomystes to family rank on account of its dentiferous 
maxillary. The transitions from one family to another are, in most 
cases, very gradual. 
How far paleontology will bear out the system here proposed re- 
mains to be seen. 
The following diagram represents the inter-relation of the families | 
of Nematognathi and subfamilies of Siluridee and Pygidide: 
“American Naturalist, July, 1888. 
