22 



THE NAUTILUS. 



Table No. 2. Number of Eggs of Amnicola on Plants. 

 Plant. Size. No. of Eggs. 



Vallisneria spiralis 70 x 5 mm. 44 



70 X 5 mm. 27 



153 X 5 mjn. 257 



140 X 5 mm. 58 



140 X 5 mm. 222 



89 X 5 mm. 23 



53 X 5 mm. 93 



Potamogeton perfoliatus, leaf . . 64 x 10 mm. 16 



135x28 mm. 150 



25 X 5 mm. 21 



Potamogeton perfoliatus, stem . . 72 x 2 mm. 42 



Potamogeton robbinsii, leaf .... 19 x 10 mm. 55 



" " 38x10 mm. 42 



Scirpus occidentalis 95 x 12 mm. 33 



111x12 mm. 54 



77 X 6 mm. 76 



77 X 8 mm. 141 



Scirpus americanus Ill x 3 mm. 200 



lllx 3 mm. 36 



165 x 3 mm. 150 



Quantitative studies show that Amnicola is the dominant 

 genus of mollusks in the part of Oneida Lake examined, and 

 the vast number of the eggs of this snail indicates that the 

 group is fully maintaining itself. This fact is of importance 

 economically, as several fish of food value — perch, pumpkin- 

 seed, bluegill, sunfish, catfish, sucker — as well as a few smaller 

 fish preyed upon by larger and valuable food fish, use these 

 snails as food. The eggs of Amnicola were observed in mid- 

 summer (July 25 to Aug. 4), and the condition of the em- 

 bryos (in the trochosphere stage) indicate that they would be 

 hatched from the middle to the latter part of August. 



EXPLANATION OF FIGURES, PLATE 2. 



1. Eggs of Gillia altUis on leaf of Scirpus smithii. 



2. Eggs of Gillia altilis on leaf of Vallisneria spiralis. 



3. A single egg of Gillia on leaf of Vallisneria. 



4. Embryo of Gillia about ready to hatch. 



5. Embryo of Gillia in resting position. 



