FIG. 147.—An African Catfish, _Chlarias breviceps_ Boulenger. Congo River. Family _Chlariidæ_. (After Boulenger.) ] Allied to this group is the family _Pygidiidæ_ with a differently formed bony capsule and no adipose fin. The numerous species are all South American, mostly of mountain streams of high altitude. Some are very small. Certain species are said to flee for protection into the gill-cavity of larger catfishes. Some are reported to enter the urethra of bathers, causing severe injuries. The resemblance of certain species to the loaches, or _Cobitidæ_, is very striking. This similarity is due to the results of similar environment and necessarily parallel habits. The _Argidæ_ have the capsule of the air-bladder formed in a still different fashion. The few species are very small, inhabitants of the streams of the high Andes. =The Loricariidæ.=—In the family of _Loricariidæ_ the sides and back are armed with rough bony plates. The small air-bladder is still in a bony capsule, and the mouth is small with thick fringed lips. The numerous species are all small fishes of the South American waters, bearing a strong external resemblance to _Agonidæ_, but wholly different in anatomy. =The Callichthyidæ.=—The _Callichthyidæ_ are also small fishes armed with a bony interlocking coat of mail. They are closely allied to the _Pygidiidæ_. The body is more robust than in the _Callichthyidæ_ and the coat of mail is differently formed. The species swarm in the rivers of northern South America, where with the mailed _Loricariidæ_ they form a conspicuous part of the fish fauna. [Illustration: FIG. 148.—_Loricaria aurea_ Steindachner, a mailed Catfish from Rio Meta, Venezuela. Family _Loricariidæ_. (After Steindachner.) ] =Fossil Catfishes.=—Fossil catfishes are very few in number. _Siluridæ_, allied to _Chlarias_, _Bagarius_, _Heterobranchus_, and other fresh-water forms of India, are found in the late Tertiary rocks of Sumatra, and catfish spines exist in the Tertiary rocks of the United States. Vertebræ in the Canadian Oligocene have been referred by Cope to species of _Ameiurus_ (_A. cancellatus_ and _A. maconnelli_). _Rhineastes peltatus_ and six other species, perhaps allied to _Pimelodus_, have been described by Cope from Eocene of Wyoming and Colorado. _Bucklandium diluvii_ is found in the Eocene London clays, and several species apparently marine, referred to the neighborhood of _Tachysurus_ or _Arius_, are found in Eocene rocks of England. There is no evidence that the group of catfishes has any great antiquity, or that its members were ever so numerous and varied as at the present time. The group is evidently derived from scaly ancestors, and its peculiarities are due to specialization of certain parts and degeneration of others.