Introduction. xlv 



Philypnus dormitor (Lacepede): Motzorongo; Obispo; Perez. 

 Dormitator maculatus (Bloch) : El Hule; Obispo; Perez. 

 Chonophorus taiasica (Lichtenstein): Perez. 

 Achirus fasciatus Lacepede: Perez. 



RIO SAN GERONIMO SYSTEM. 



This stream was visited at San Geronimo. It is a small river 

 flowing with considerable current over a sandy bottom. 



The following is a list of the species taken from it: 

 Tetragonopterus asneus Giinther: San Geronimo. 

 Roeboides guatemalensis (Giinther) : San Geronimo. 

 (Crambusia fasciata Meek: San Geronimo. 

 Heterandria pleurospilus (Giinther) : San Geronimo. 

 Pcecilia sphenops Cuvier & Valenciennes: San Geronimo. 

 Siphostoma starksi Jordan & Culver: San Geronimo. 

 Cichlasoma mojarra Meek: San Geronimo. 

 Cichlasoma melanurum (Giinther) : San Geronimo. 



RIO TEHUANTEPEC SYSTEM. 

 I visited this river at Tehuantepec. Its water was low, flowing 

 over a sandy bed with a moderate current. 



The following fishes are known to occur in this river : 



Tetragonopterus aeneus Giinther: Tehuantepec. 

 ,Gambusia fasciata Meek: Tehuantepec. 



Anableps dovii Gill: Tehuantepec; Tequisistlan. 

 ^Heterandria lutzi Meek: Tehuantepec. 

 \Poecilia sphenops Cuvier & Valenciennes: Tehuantepec. 



Mugil cephalus Linnaeus: Tehuantepec. 



Cichlasoma evermanni Meek: Tehuantepec. 



Philypnus dormitor (Lacepede) : Tehuantepec. 



RIO VERDE SYSTEM. 

 The Rio Verde is a small Pacific coast stream heading a short dis- 

 tance above Oaxaca. When we visited this stream near Oaxaca it 

 was nearly dry; its bed being broad and covered with sand. A few 

 holes in the bed contained a few small fishes belonging to two species. 

 Tetragonopterus aeneus Giinther: Oaxaca. 

 Fundulus oaxacae Meek: Oaxaca. 

 (Heterandria lutzi Meek: Oaxaca. 



RIO BALSAS SYSTEM. 

 The Rio Balsas is the second largest river in Mexico, which flows 

 into the Pacific Ocean. It drains most of the area between the zone 

 of recent volcanoes, which forms the water-shed between it and the 

 Rio Lerma, and the Sierra Madre del Sur. The water in all the trib- 

 utaries examined by me is clear and flows over a sandy or rocky bot- 

 tom. In comparison to the size of this river the number of species 

 of fishes known from it is small. 



