6 E. B. Williamson and J. H. Williamson 



the Rio Negro and the Magdalena, the other probably by way of the Rio 

 Braiico and Guianan rivers. At least the southern tributaries of the 

 Orinoco should yield some species of Perilestes but at present none is 

 known from Venezuela. 



The southern Group II has its headquarters in the Amazonian basin. It 

 is probably older and is certainly not as homogeneous as Group I. One 

 very distinct species, fragilis, which about equals in size the larger species, 

 remotus and magdalenae of Group I, is, like these two species, the most 

 widely separated from the Amazonian basin, being known only from the 

 vicinity of Rio Janeiro. Its nearest rival in size in its group is kalili, prob- 

 ably its nearest relative, also a very distinct species, and also one on the 

 fringe of the geographical distribution of the group, being known only 

 from the Madeira River in Matto Grosso, and from the Rio Japacani in 

 eastern Bolivia. Another very distinct species of the group is attenuatus. 

 In fact, as regards probable relationship with other species of the group, 

 it is the most distinct of all. It has a wide distribution, occurring on 

 the Rio Beni in Bolivia, on the Madeira at Porto Velho, Amazonas, on the 

 Rio Negro at IManaos, and on the lower Amazon at Santarem. The two 

 remaining species of the group, solutus and minor, are closely related. 

 Solutus occurs on the Madeira River in IMatto Grosso, and its range ex- 

 tends southward into the Paraguay in the same state. It is also probably 

 along the entire lower Amazon as it has been taken at Para. 3Imor is the 

 smallest species of the genus and is known only from the IMadeira River 

 at Porto Velho, Amazonas. 



Habits 



All Perilestes are forest stream dwellers. The small creeks where we 

 have invariably found them may be briefly described. The three streams 

 at Cristalina, Colombia, have been described in Misc. Publ. No. 30, Univ. 

 of Mich., Mus. of Zool. To briefly summarize this description, the creeks 

 flow in a rolling or hilly, heavily forested country at an elevation of 

 about 320 meters. They vary in size from a few inches to ten or twelve 

 feet in width. Generally the flow is gentle, pools alternating .with short 

 ripples. The beds are mixed mud and gravel. The flora is rich with over- 

 hanging bushes and clumps or stretches of aquatics. "VMien we collected 

 there the streams were at low water stage and the water was clear. This 

 description will do equally well for the two streams in the Canal Zone, 

 Panama, where we found Perilestes. In Brazil, similar streams were 

 found at Porto Velho (60 meters above sea level), Albuna, Villa Murtinho, 

 Manaos and Para, each inhabited by from one to three species of Perilestes. 

 The streams near Cashuelo E.speranza, Bolivia, contained a few outcrop- 

 pings of rock but otherwise fell within the general description given above. 

 On Mt. Tijuca, in the vicinity of Alto Boa Vista, a suburb of Rio de 

 Janeiro, there are several creeks about one foot deep, varying in width 

 from eight to twenty feet and having a rapid descent among boulders 

 and outcroppings of solid rocks. Perilestes was found in limited num- 

 bers along the wooded portion of these creeks. 



