2 24 Field Museum of Natural History — Zoology, Vol. X. 



That the faunas of these small streams are of much interest is indicated 

 by the fact that Hoplosiernum punctatum sp. no v. belonging to a dis- 

 tinctly South American family, of which heretofore no representative 

 was known north of the Rio Atrato Basin in Colombia, was taken in 

 the Rio Marte Arnade, a small stream, about 6 miles east of Panama 

 City, and was not seen elsewhere in Panama. Gephyrocharax inier- 

 medius sp. nov. was found only in the Rio Chame; Bryconamericus 

 cascajalensis sp. nov. only in the Rio Cascajal at Porto Bello; Rivulxis 

 hrunneiis Meek & Hildebrand only in a small coastal stream at Toro 

 Point and Microeleoiris panamensis gen. et sp. nov. only in the Rio 

 Juan Diaz and the Rio Chorrera. Ancistrus chagresi, which is com- 

 mon in the Rio Chagres Basin, was taken on the Pacific slope only 

 in the Rio Chorrera. 



The Rio Chagres and Its Fauna. 



The Rio Chagres is but slightly affected by tides at its mouth, as 

 there is a difference of less than two feet between mean high and mean 

 low water on the Atlantic coast of Panama. Ascending this stream, it 

 is found to flow through a low swampy region in its lower course, or as 

 far as Gatun. Here it receives its largest tributary, the Rio Trinidad, 

 which is a sluggish stream winding its way for many miles southward 

 through a low, dense jungle where mosquitoes abotmd in countless 

 numbers. It reaches the mountains opposite the Rio Chorrera. In 

 the upland regions it is free from rapids, but the current is swift. 



At Gatun the Rio Chagres receives another tributary of considerable 

 size, namely, the Rio Gatun, which assiunes an easterly coiirse, and is a 

 clean, clear stream, usually with sandy or pebbly bottom and without 

 rapids or falls but with a strong current. 



Following again the course of the Rio Chagres from Gatim upward 

 it assumes the general direction of the present Canal, i. e., southeast- 

 ward until Gamboa is reached where it makes a rather sharp turn to the 

 left and then follows an east by northeast course. As far up as Alha- 

 juela or about 50 miles from its mouth, following the winding cotu^se of 

 the stream, the current is swift but no rapids occur. From this point 

 upward it becomes swifter and at intervals rapids appear which can 

 be crossed only when the water is at a low stage. At San Juan, the 

 last native village on the river, the stream forks ; the left fork is known 

 as the Rio Pequeni which soon again divides forming the Rio Boqueron 

 and the Rio Pequeni. The fork to the right, going up stream, at the 

 village of San Juan is the Upper Chagres. Following its course the 

 mouth of a large tributary is soon reached. This is the Rio Indio which 

 has a waterfall a short distance above its mouth; below it a large num- 



