126 FIELD COLU.MIUAN ML'SEUM ZOOLOGY, VOL. III. 



fishes perish. They are, however, present everywhere to establish 

 themselves in every body of water which may carry them through 

 to the next rainy season. 



The larger number of the Pivciliida are mud-eating fishes. A 

 few, such as Zoogoneticus, are carnivorous. 



The gestation of many tropical fishes present some strange 

 peculiarities. Some of the Silurida carry the eggs in the mouth 

 till hatched, while a few others are thought to be viviparous. 

 Viviparity among the tropical Picciliida seems to be the rule 

 rather than the exception. It would seem that in the tropical 

 fresh waters of America, there is much more provision made for 

 the care of the young than in the cooler waters of the Northern 

 continent. 



It was rather surprising to find such a large number of Cliiros- 

 toina in the Lerma Basin and the probability is that this number 

 will be considerably increased when this basin is more thoroughly 

 explored. I had seen but a few specimens of Chirostoma before 

 going to Mexico, and so never had an opportunity to study these 

 fishes. And while I was careful to pick up specimens of all species, 

 yet my unfamiliarity with the group, no doubt, caused me to over- 

 look some species. Again there is a number of small isolated 

 lakes which have never been visited. Most of these lakes, no 

 doubt, as do Patzcuaro and Zirahuen, have in them one or 

 more characteristic species. This river system is far from 

 being thoroughly explored. While its species are about one- 

 third the number of those found in the YVabash River in Indi- 

 ana, its fish fauna is quite as distinct and characteristic as 

 if it were an island in the sea. Considering this basin as a 

 whole, taking note of its spring brooks and running waters and its 

 sluggish streams; its lakes, some with outlets, others without out- 

 lets; some fresh, others quite brackish; its interesting and peculiar 

 fish fauna is certainly inviting to the student engaged in the study 

 of variation. 



The Rio Balsas is one of the largest rivers in Mexico. It is 

 southeast of the Lerma and drains about the same area; and 

 though these two rivers are so near each other, not a single species 

 of fish is known to be common to both. At present but ten species 

 are known from the Balsas Basin. But one species of the Ather- 

 inidie and two of the Pa'ci/iidte, are known from the Balsas, and yet 

 these two families comprise nearly two-thirds of the fishes of the 

 Lerma Basin. The Balsas is far from being thoroughly explored; 



