Localities in which Pellagra is Prevalent. 65 



having been cleared along the hne of travel of its coating of 

 algae and slime. This coating of the rocks was everywhere 

 present, and seems to furnish food to a host of microscopic 

 animals, and some larger ones, including some of the insects. 

 A large percentage of it consists of algae and protozoa, and 

 grazing animals, such as the snails, find it nutritious forage 

 easily obtained. Several other species of snails (Physa sayi 

 and Planorbis hicarinatus among them) were collected, and 

 a small elongate clam. The collection, however, gives a 

 wholly inadequate idea of the molluscan fauna of the 

 streams. The material collected was merely picked up inci- 

 dentally and because it chanced to catch my attention when 

 searching for other things. 



The shells mentioned were identified by Drs. Pilsbry 

 and Sterki. 



FISHES. 



The community of insects and other animals, of which 

 Simulium larvae form a part, inhabiting the rapids of our 

 mountain streams, is relatively free from the attacks of the 

 larger fishes. Such fishes cannot follow them here. Frogs 

 and water birds, also, have little chance to get them, hidden 

 as they are in narrow spaces among the rocks and generally 

 clinging to the under surfaces. Even the larger carnivorous 

 beetles and bugs, such as Dytiscus and Belostoma, cannot 

 maintain themselves in the rapids, and the small species 

 suited to the peculiar situation are thus here as nowhere 

 else in our waters free from their attacks. A single family 

 of fishes, however, contains members that have been driven 

 like the insects in the struggle for existence to these same 

 waters, and has become adapted to the peculiar conditions 

 here prevailing. The sand darters (Etheostomatidee) are 

 very small often brightly colored fishes, the largest reaching 

 a length of six inches or thereabouts, that habitually lurk in 

 shallow running waters, many of them under rocks in the 

 swiftest streams. They are relatively slender, often with 

 pointed snouts, and naked napes, the scales being gone as if 

 rubbed away by probing under stones for shelter and food. 



