The Food of the Smaller Fresh - Water Fishes. 
69 
Four specimens from Rock River, and one from Cedar Lake, in 
Lake County, had divided their food about equally between plant 
and animal substances: the former, consisting wholly of filamen- 
tous Algm, taken by four of the specimens in quantities to make 
it certain that they were ingested purposely. The animal food 
was about equally insects and crustaceans, the former nearly all 
aquatic larvae of Diptera (Chironomus being the commonest form), 
and the latter chiefly Entomostraca, of which Cladocera were the 
most abundant. One of the specimens had eaten Cypris — some 
of them Cypris vidua. Cyclops was also noticed in three of the 
fishes, and amounted to three per cent, of the food. 
The herbivorous character of this fish seems not to be related to 
any structural facts ; but the occurrence of the large ratio of En- 
tomostraca is at once accounted for by the well-developed gill- 
rakers, these serving as a straining apparatus by means of which 
the fishes possessed of it are able to appropriate minuter organ- 
isms than would otherwise be available for their food. 
Pygosteus pungitius, Lac. Many-Spined Stickleback. 
This species has hitherto been found by us only in Lake Michi- 
gan, and in Calumet River near its mouth. 
But two specimens were dissected; and these had fed wholly 
on larvas of Chironomus and Simulium (sixty per cent.), and on 
Chydorus and other Cladocera (forty per cent.). 
With so small an amount of material to illustrate the food of 
the family, we can only say that it evidently consists chiefly of 
aquatic larvae and Entomostraca, together with a considerable per- 
centage of vegetable substances. In the absence of any appara- 
tus for mastication, the latter will doubtless be found to consist of 
Algae, as in the cases examined. 
FAMILY ATHERINIDiE. 
Labidesthes sicculus, Cope. Silversides. 
This elegant little fish, the only fresh-water representative of 
its family, is generally abundant throughout the State, and has 
been collected by us in a great variety of situations, from the 
northern lakes to the Wabash River. 
It is long and slender, the mouth small and well furnished with 
