AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
225 
In the open water there was always a very fair supply of entomostraca, both 
Cladocera and Diaptomi , but at the time of our arrival on the West Bay the phenom- 
enal fact was the vast abundance, both in deep and shallow water, of a rotifer or 
wheel animalcule which forms rolling spherical colonies imbedded in a gelatinous 
medium, each colony consisting of a little cluster of these animalcules arranged in 
such a manner that their inner ends approach each other in the middle of the mass, 
while their outer ends, with mouths, cilia, etc., are exposed on the surface. To the 
naked eye these colonies of rotifers appear like minute grayish specks of floating 
matter. This species belongs to the genus Conochilus , but differs noticeably from the 
common C. volvox. I have thought best, consequently, to describe it as C. leptopus 
(page 256). It was so abundant in the water that a haul of a ring net, a foot across, 
for fifty strokes of a single pair of oars gave a measured half pint of this form alone. 
This colonial rotifer is not to be confounded with the “water bloom,” which devel- 
oped in Yellowstone Lake a little later to an extent very embarrassing to our surface 
net work. This so-called “ bloom” consisted of specks of various alg;e growing so freely 
in the water as to give it a faiut, tint of dirty green, and washing ashore in quantity 
along the leeward side of the lake, usually at this season the northern and eastern. 
Away from the shore, by far the most common crustacean was Daplinia pulex.* 
Although in ordinary situations the males of Daplinia are by no means common, 
in our Yellowstone Lake collections, made in August and September, the males of this 
variety were many times commoner than the females, making sometimes nearly the 
whole of a large catch. The few examples of the other sex seen were mostly young, 
although a female bearing the ephippium occurred occasionally. Next in abundance 
was the smaller of the Diaptomi found in Shoshone Lake, the so-called variety of D. 
siciiis, and with this came somewhat rarely, but still fairly abundant, D. shoshone and 
D. lintoni. Several species of Cyclops occurred here, only a new one ( C. minnilus) 
very frequently, however, and this in small proportion. 
Most of these crustaceans ranged in shore as well as in the deeper water of the 
interior parts of the lake, Daplinia pulex falling away in numbers more rapidly in 
shallow-water collections than Diaptomus siciiis. To these inshore species we may 
add, from our surface-net collections, Polyphemus pediculus (sometimes very abundant 
among the weeds), Cyclops yyrinus, and C. serrulatus (both rare), Chydorus sphcericus 
(few), Scapholeberis mucronatus (few), Cypris sp. (only occasional), Alona , and the usual 
miscellaneous drift of shore forms, Chirononius , Allorcliestes (both dentatus and inermis ), 
Gammarus , caseworms, hydrachnids, planarians, Clepsine , etc. 
Collections made in the lake near enough to the outfiow of hot springs to exhibit 
their influence differed from those made in cold water only in their more scanty char- 
acter; and where the water was actually warm it commonly contained nothing but the 
'The common and even abundant occurrence of this species in Yellowstone Lake as a form 
apparently pelagic in its habits (widely contrasted, consequently, with its usual character) was so 
unexpected and unusual that I hesitated long before assigning this Daplinia to the species most abun- 
dant in our stagnant pools. Prolonged study of it. from various collections in the Park in comparison 
with those from the waters of Illinois, has finally led me to conclude, however, that this Yellowstone 
Lake form is not to he specifically distinguished from American examples of pulex. In order to 
furnish material for a more critical comparison than has hitherto been made of the American and 
European representatives of this species, I append a description, under the varietal name of pulicaria, 
based upon Yellowstone specimens, with figures of both sexes (page 242 and plate xxxvu, fig. 1). 
F. C. B. 1891 15 
