216 BULLETIN OF THE UlftTED STATES FISH COMMISSION. 



The assemblage of animals in this lake offered a peculiarly interesting subject of 

 study, since it included practically no aquatic vertebrates. There were, of course, no 

 fishes at all ; we saw no turtles or water snakes, but a single frog, and only one small 

 salamander. The dominant groups were insect larvae, leeches, amphipod crustaceans, 

 and entomostraca. By far the most ab undant aquatic insects were caseworms (larval 

 Phryganeidw), mostly pupae at the time of our visit. There were no crayfishes and 

 no isopod or phyllopod crustaceans; but two amphipod genera (Oammarus and 

 Allorchestes) were very abundant. The Gammari, represented by a single large and 

 robust species (Oammarus robustus Sin.), were exceedingly common, creeping or swim- 

 ming about, on or near the bottom, inshore, especially where collections of debris from 

 the inlet rested in hollows of the rippled sand. They sometimes rose to the surface 

 at night, where our towing net occasionally took a surprising number of them at 

 one haul almost nothing else. They occurred also abundantly i n our deepest dredg- 

 ings, in the lagoons examined and in the streams flowing into the lake. 



This lake seemed, indeed, a paradise for the Gammari, containing an abundance 

 of food for them, both animal and vegetable, fresh and in process of decay, and 

 scarcely anything that fed upon them in turn. The commonest large leech (Nephelis 

 obscura, var. maculata) feeds upon them to some extent, as I found by the dissection 

 of two specimens; but another of these leeches voided a large horse-fly larva 

 (Tabanus). Their own food, if I may judge from that of seven specimens which I 

 dissected, is quite varied, consisting of rotting vegetation (whose condition was shown 

 by the mycelial threads running through it), of fresh algiB, and other green-plant 

 substance, and of entomostraca (Diaptomi as far as seen). The stomachs of three con- 

 tained, also, a noticeable amount of pollen grains of the pine. In three of the seven 

 specimens examined large numbers of Grcgarlncc infested the intestine. Their prob- 

 able effect was shown by the fact that the intestine was empty in two of the para- 

 sitized specimens. Our Gammarus was thus practically at the head of the biological 

 system of this lake, which was for it a royal domain where it was free to exact tribute of 

 all, yielding scarcely anything itself in turn. The females at this time had their brood 

 cavities loaded with young. 



The entomostraca were principally a single species of copepod a very large blood- 

 red Diaptomus, new to science and here described as D. shoshotie. This occurred in 

 great numbers in several hauls with the surface net, and could usually be seen on a 

 calm evening near the surface, where its tiny sportive leaps in the air kept the water 

 microscopically agitated, as if by minute fish. Another Diaptomus, near D. sicilis and 

 perhaps a variety of that species, occurred much more sparingly, and a third species 

 of this genus, described on p. 252 as D. lintoni, was less frequently seen than either of 

 the foregoing. There were a few species of Cyclops here, G. serrulatus Koch, C. gyrinus 

 Forbes, C. minnilus (new), and perhaps others; also, a Oypris, a Bosmina, a Chydorus, 

 a Daphnia (D. pulex), and Polyphemus pediculus. So far as the Crustacea were con- 

 cerned, the lake was in practical possession of Gammarus robustus and Diaptomus sho- 

 shone. 



