THE NAUTILUS. 19 



NOTES ON NIDIFICATION IN GILLIA AND AMNICOLA. 



BY FRANK COLLINS BAKER. 



Observations on the nidification and embryology of our 

 American fresh- water mollusks are rare ; and contributions to 

 our knowledge of this subject, though they may not be exten- 

 sive, are of value. With this need for additional knowledge 

 in mind, the writer ventures to present the following frag- 

 mentary notes on the nidification of two common genera of 

 American Amnicolidae, two species of which have but recently 

 been described. 



The observations were made while conducting quantitative 

 studies of the animal life of Oneida Lake, New York State's 

 largest inland body of water. The eggs of four genera of 

 mollusks were observed at this time (the latter part of July 

 and the first part of August), Gillia, Amnicola, Galba, and 

 Physa. Only the first two genera are considered in this paper. 

 It was hoped that time would permit a more extensive study 

 of these embryos, but the quantitative studies extended to 

 such a late date that there was no opportunity to carry on 

 the very interesting studies on the development of these 

 snails, which would have been of great interest and some 

 value. The information gathered, however, may be consid- 

 ered a contribution to our knowledge of the embryology of 

 these mollusks and may stimulate other students to a study 

 of our fresh- water gastropods. 



Gillia, altilis (Lea). PI. 2, figs. 1-8. 



Gillia altilis is a very common species in Oneida Lake in 

 the quiet bays, among vegetation. Egg-laying apparently 

 takes place late in June or early in July. In eggs examined 

 July 31st, the embryos were nearly ready to be hatched, the 

 embryonic shell being fully formed. Eggs were observed on 

 six species of plants; Vallisneria spiralis (abundant near 

 base), Pomatogeton robbinsii (on lower three or four leaves), 

 Potamogeton perfoliatus, Scirpus smithii, Scirpus americanus, 

 and Sagittaria latifolia. 



The eggs are laid singly (never in a capsule as in the 



