CAT-FISHES. 581 



VII, SiLURiD^ Opisthopter^. — The rayed dorsal fin is 

 always present, sliort, and placed above or behind the middle 

 of the length of the body, above or behind the ventrals which, 

 however, are sometimes cdjsent ; anal short. Nostrils remote 

 from each other ; if a nasal barbel is present, it belongs to the 

 anterior nostril. Lower lip not reverted. The gill-membranes 

 are not confluent xoith the skin of the isthmus : Nematogenyina 

 and Trichomycterina. 



The genera Heptapterus, Nematogcnys, Trichomycterus, Ere- 

 mophilus, and Pariodon, belong to this sub-family. They 

 are small South American Siluroids, the majority of which 

 inhabit waters at high altitudes, up to 14,000 feet above 

 the level of the sea. In the Andes they replace the Loaches 

 of the Northern Hemisphere, which they resemble in appear- 

 ance and habits, and even in coloration, offering a striking 

 example of the fact that similar forms of animals are pro- 

 duced under similar external physical conditions. 



VIII. SlLURiD^ Branchicol/E. — The rayed dorsal fin is 

 present, short, and p)laccd behind the veiitrals ; anal short. Vent 

 far behind the middle of the length of the body. Gill-mem- 

 branes confluent with the shin of the isthmus. 



Stegophilus and Vandcllia, two genera from South America, 

 comprising the smallest and least developed Siluroids. Their 

 body is narrow, cylindrical, and elongate ; a small barbel at 

 each maxillary ; the operculum and inter-operculum are 

 armed witli short stiff spines. The natives of Brazil accuse 

 these fishes of entering and ascending the urethra of persons 

 while bathing, causing inflammation and sometimes death. 

 This requires confirmation, but there is no doubt that they 

 live parasitically in the gill-cavity of larger fishes {Platy- 

 stoma), but probably they enter these cavities only for places 

 of safety, without drawing any nourishment from their 

 host. 



