216 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The assemblage of animals in this lake ottered 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 abundant aquatic insects were caseworms (larval 
Phryganeidce ), mostly pupae at the time of our visit. There were no crayfishes and 
no isopod or phyllopod crustaceans; but two amphipod genera ( Gammarus and 
Allorchestes) were very abundant. The Gammari, represented by a single large aud 
robust species ( Gammarus robustus Sm.), were exceedingly common, creeping or swim- 
ming about, ou 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 (JSfephelis 
obscura, var. maculata ) feeds upon them to some extent, as 1 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 algae, 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 Gregarince 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 liad their brood 
cavities loaded with young. 
The entomostraca were principally a single species of copepod — a very large blood- 
red Diaptomus , uew to science and here described as D. shoshone. 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. sieilis 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, C. serrulatus Koch, C. gyrinus 
Forbes, G. minnilus (new), and perhaps others; also, a Gypris , 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. 
