208 EIGENMANN— YELLOW FEVER AND FISHES. 



name " bagre " is used almost everywhere in Latin America, but is 

 applied to a great variety of different catfish-like fishes. If the 

 " life " of northern Peru shares its habit of eating mosquito larvae 

 with the rest of the members of the genus Pygidium, it is a most 

 important discovery. Various species of Pygidium are found in all 

 the mountain streams of South America and a few are found in the 

 hot lowlands of the Amazon Valley. It belongs to a peculiar family 

 of South American catfishes which are called " bagre," " bagrecitos," 

 "capitan," etc. I monographed the family. ("The Pygidiidse, a 

 family of South American Catfishes," Mem. Carnegie Mus., VII., 

 No. 5, pp. 259-398, Plates XXXVI.-LVI., 1918.) 



In Arequipa I caught specimens of another species of " life," 

 Pygidium quechiwrum, in such numbers that a devout passer-by ex- 

 claimed, " It exceeds the miraculous draft of St. Peter ! " 



The underlying structure of most of the members of the family 

 is the presence of spines on the opercle and interopercle and the pres- 

 ence of two barbels at the end of the maxillary where other catfishes 

 carry but one barbel. The underlying habit is their eel-like move- 

 ments and their ability to hold an advance, once gained, by means of 

 the spines on the head. They get under and between rocks, eel their 

 way into holes, and can climb vertical walls. 



The queerest members of the family live as commensals or para- 

 sites in the gill cavities of larger fishes, and some of them have gained 

 an evil reputation and struck terror into the natives of the entire hot 

 country by the reputed habit of entering the urethra of bathers, some- 

 times requiring operations or causing death. 



Of the genus Pygidium about 70 species are known. They range 

 from a few millimeters to 390 mm. in length and are found from 

 sea level to at least 12,000 feet. They are abundant in and about 

 Lake Titicaca. I caught them in southern Chili to northern Colombia 

 and Guiana. They are also abundant in the mountain streams of 

 southeastern Brazil. The other four species of fishes tried in north- 

 ern Peru and sent by Dr. Hanson are : 



I. The "bagre." This is Pimelodella yuncensis Steindachner 

 confined to the rivers between Pacasmayo and Paita. It may be 

 found as far south as the Rio Santa. It is not found in the Rimac. 



