88 Thirty-second Report on the State Museum. 



Lesu.), but the larger number are injurious to flshes, in attaching themselves to 

 them and sucking their blood ; in being, by nature, parasitic upon them, and by 

 destroying insect larvae and mollusks which constitute so large a proportion of 

 fish food. They at times occur in almost incredible numbers, as related by J. 

 W. Milner,* when, on one occasion, in the month of April, as some fishermen 

 were lifting their nets from about fifty fathoms, some fifteen miles out from 

 Kenosha, Wis., a species of Ichthyobdella [} Milneri of Verrill] so thickly cov- 

 ered the fishes (trout, white-fish and cisco) and the nets, that they fell to the 

 deck in such numbers that it became slippery, and an old coat was thrown down 

 for the man to stand upon who was lifting the gang. 



- MOLLUSCA. 



No special effort was made to collect the Mollusca of the waters. Two 

 species, Physa heterostropha and Limnoea desidiosa were observed abundantly 

 on sticks and pieces of timber in the water. In the bed of a small stream near 

 the hatching-house, where the current was interrupted by scattered blocks of 

 stone, a marl-like deposit occurred, consisting almost entirely of small shells and 

 comminuted larger ones, into which the hand could be thrust to the depth of 

 several inches. Specimens of this deposit were brought with me, and its exam- 

 ination disclosed the following species — authoritatively determined by Dr. James 

 Lewis, of Mohawk, N. Y. : 



Helodiscus lineatus Say, Limnasa catoscopium Say, 



Helix albolabris Say, Limncea desidiosa Say, 



Helix alternata Say, Limn ma humilis Say, 



Pupa corticaria Say, Physa, heterostropha Say, 



/Succinea ovalis Gould, Gyraulus parvus Say, 



Zonites nitidus Muller, Bythinella obtusa Lea, 



Zonites arborea Say, Splioerium sp. ?, 



.Carychiuu exiguum Say, Pisidium abditum, Hald. 



None of the above species are of special rarity, but are such as occur in 

 various limestone regions throughout the State. 



The Physa heterostropha and Limncsa desidiosa, which were taken from the 

 waters in their living state, were brought to Albany and placed in a small aqua- 

 rium. From that time (early in December) to the present, clusters of eggs 

 have been deposited on the surface of some thin pieces of wood floating on the 

 water, and occasionally on the glass sides of the aquarium just at the surface of 

 the water. From these eggs, many hundreds of young have been produced, 

 during the past three months. The clusters, which are believed to be of both 

 species, are transparent, gelatinous masses of about one-half of an inch long, with 

 a breadth of from one-third to one-half their length, enveloping the transparent 

 eggs, which show distinctly, at first, the milk white interior nucleus. 



Having, in the preceding pages, referred to the various forms of animal life 

 populating the waters of Caledonia creek, and, in addition, presented brief state- 

 ments of their appearance, habits, transformations and classification, to aid in 

 their recognition, and with a view of lending additional interest to their study, 

 it may be proper to devote a few pages to a consideration of the economic value 

 of the several classes in their connection with fish-culture. 



CRUSTACEANS AS FOOD FOR FISHES. 



It is almost unnecessary to state the fact that the appearance, condition and 

 quality of fish are greatly influenced by the nature of their food. One of your 



* Report U. S. Commission of Fish and Fisheries, 1872-73, p. 64. 



