178 TEE AMERICAN NATURALIST [Vol. XLV 



loids. After a careful examination under the microscope 

 I have been unable to find any constant differences be- 

 tween shells of the same age, except that the larger 

 specimens of Ancylus seem to have grown continuously 

 and evenly, while those ancyloids which attained a 

 G-wifUachia stage show the sharp contrast between the 

 separate stage and that with the expanded third stage 

 of the shell. As this is only what one might expect if the 

 Ancylus attained its full growth without interruption, 

 while the ancyloid becoming septate passed through a 

 resting stage and then began to grow again, I consider 

 this difference of no moment systematically. The young 

 Ancylus and the ancyloid of the same length appeared 

 generally quite identical, though I noticed that in both 

 the obliquity of the apex varied to some extent, being 

 more emphatically bent toward the posterior right side 

 in some individuals than in others. 



Ancylus meekiana is, when young, for a time nearly 

 parallel-sided, the growth toward maturity being more ex- 

 panded than at first. The apex is behind the middle of the 

 shell and slightly inclined toward the posterior right-hand 

 side at maturity. The microscope reveals some very 

 feeble radial striae from the apex, mostly vanishing be- 

 fore they reach the base. The incremental lines are not 

 strongly marked and the shell when clean is of a pale 

 translucent yellowish color. At or near maturity the 

 shell assumes a more oval form slightly more expanded 

 in front than behind. The animal has short pointed 

 tentacles, well-marked black eyespots, and a bluish-white 

 color, except about the mouth, where the yellow-brown 

 jaws are laterally set and the buccal mass has a pinkish 

 color. The shell is about 3.6 mm. long, 2.3 wide, and 1.0 

 high. In the dark-colored specimens of the wild Ancylus, 

 on the inside, may often be seen a dark-brown line cor- 

 responding to the margin of the young Ancylus and 

 showing the more parallel-sided early outline. 



Miss Mary Breen, who has been studying the anatomy 

 of the fresh-water gastropods of the District of Go- 



