117 



Its mouth is small ; the gill-rakers are long and slender (about 

 half as long as the corresponding filaments), but are not unusually 

 numerous; the pharyngeal apparatus is insigniiieant or wanting; 

 and the intestine is short and simple, not longer than the head and 

 body together. 



Four specimens from Eock 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 filamentous 

 Alga), taken by four of the specimens in quantities to make it 

 certain that tbey were ingested purposely. The animal food was 

 about equally insects and crustaceans, the former nearly all aquatic 

 larvre of Diptera (Chironomus being the commonest form), and the 

 latter chietiy EntomostracR. of which Cladocera were the most 

 abundant. One of the specimens had eaten Cypris — some of them 

 Cyprls vidua. Cyclops was also noticed in three of the hshes, 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 organisms 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 

 larvae of Chironomus and Simalium (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 

 ]s,YVie and Entomostraca, together with a considerable percentage of 

 vegetable substances. In the absence of any apparatus for masti- 

 cation, the latter will doubtless be found to consist of Algae, as in 

 the cases examined. 



Family ATHElilNIDJi. 



Labidesthes sicculus. Cope. Silversides. 



This elegant little hsh, the only local representative of its family, 

 is generally abundant throughout the State, and has l)een 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 

 teeth, while the throat is destitute of special pharyngeal apparatus. 

 The gill-rakers are unusually well developed, being numerous, slender, 

 finely toothed, and longer than the corresponding filaments of the 

 gills. Taking into account the small size cf the fish, and the con- 

 sequently small diameter of the apertures of the mouth and gills. 



