eigenmann: fresh water fishes. 241 



region from the La Plata to Mexico. One of the chief features modified 

 in passing from the Tachisurinae to the Pimelodinae is the space between 

 the anterior and posterior nares. In the Pimelodinae the barbels obtain 

 their greatest specialization. The nasal barbels are, however, not developed 

 before the Bagrinae are reached, to which all the North American species 

 belong. 



From the Pimelodinae have also been derived the Doradinas, in which 

 dermal ossifications first make their appearance, although minute plates 

 are noticed along the anterior portion of the lateral line of Platystonia- 

 ticlitJiys sturio (Pimelodinae). 



In the Doradinae and the succeeding subfamilies of SiluridcB the Weber- 

 ian apparatus varies greatly and the whole group seems to be in a state 

 of unstable equilibrium. 



In the Ageneiosinae appears for the first time the great reduction and 

 splitting into lateral halves of the air-bladder. From the Ageneiosinae 

 were undoubtedly directly derived the Hypophthalmidae. 



From the primitive Ageneiosinae and Auchenipterinae have evidently 

 been derived, as a lateral offshoot, the Pygidiidce, of which the Cetopsinas 

 retain the most ancestral traits. In this family nasal barbels again appear. 

 Some members of Stegophelinae have lost the habit of free swimming and 

 live as commensals or parasites in the gill-cavity of large species of the 

 Siluridcu. 



The three remaining families were, by Dr. Giinther, united in one of 

 his inferior groups, Hypostomatina. They have little external resem- 

 blance to the Silityidce. 



The CalliclithyidcB have two series of smooth plates covering the sides, 

 while the Loricariidce have several series of rough plates. The teeth and 

 dentiferous bones of the latter have also been considerably modified. The 

 ArgidcE are dwarfed forms inhabiting high mountain streams. They are 

 naked but otherwise similar to the mailed Loricariidce. 



Family II. DIPLOMYSTID^. 



= Diplomystidce Eigenmann, Zoe, Vol. I, 14, 1890. 



Air-bladder well developed, simple or with transverse constrictions, 

 lying free in the abdominal cavity. Mouth terminal, teeth incisor-like and 

 villiform ; intestines short, arranged in longitudinal folds. Body naked. 

 Diaphragm membranaceous. Tip of scapular process touching basioccip- 



