EIGENMANN : THE PYGIDIID^, A FAMILY OF SOUTH AMERICAN CATFISHES. 261 



Nearest the Pygidiince are the Pareiodontma', which lack a nasal barbel. The 

 teeth are very peculiar and in a single series (See Fig. 21) and the gill-membranes 

 are attached. But one species is known. The Nematogenyina', Pygidiinw, and 

 PareiodonUncE are free-living, and have a terminal or subterminal mouth and pointed 

 or incisor teeth. 



The StegophiUna', V andellivna' , and Tridentince differ widely from the members 

 of the above-mentioned subfamilies in structure and habit. They are all small or 

 minute; the mouth is inferior; the head flat below; the lower barbel at the angle of 

 the mouth is minute. The jaws are weak, the teeth absent or slender. The gill- 

 opening, in all but Acanthopoma, is greatly restricted, which, put in terms of habit, 

 means that the mouth is suctorial. Some of them are parasites, or commensals. 



The Tridentinai differ in having the anal fin much longer than the others. 

 Nothing is known of their habits and they are so small (the largest known specimen 

 is but 27 mm. long) that it is a wonder that any of them have arrived in the bottles 

 of the naturalist. 



In the Vandelliince the teeth are reduced to a minimum, and the rami of the 

 lower jaw do not meet in the middle. The differences between the genera are 

 minute, but well marked. The habits of these fishes, as well as those of the next 

 subfamily, are discussed below. 



The Stegophilinw have a very large number of minute teeth in definite series 

 in both jaws. The rami of the lower jaw meet in the middle. The genus Acantho- 

 poma stands out in that its gill-membranes, while united, are free from the isthmus. 

 The genus, Henonemus, is well marked by the small number of opercular spines. 

 Ochmacanthus has numerous accessory caudal rays above and below, which make 

 the tail look like that of a tadpole. The remaining genera, Stegophilus, Homo- 

 dicetus, and Pseudostegophilus , might well be vmitcd. They differ from each other 

 largely in the position of the ventrals, the shape of the caudal, and in the number of 

 accessory rays. 



Habits. 



The habits, as well as the distribution, of various members of the Pygidiidce 

 have been derived from the general tendency of the catfishes to get under banks, 

 under logs, out of the way, and out of sight. This general tendency has been 

 modified into the specialized, insinuating habit of the Pygidiida;, for which the 

 opercular spines and the eel-like body are adaptations. 



On the plains of Bogota the Indians secured the largest specimens of Eremo- 

 philus by thrusting their arms to the bottom of holes in the banks of streams. 

 At Honda I found one species buried in the sand in the bottom of the stream. It 



