400 PROCEEDINGS OF THE ACADEMY OF [1893. 



VI — Left side of first part of radula of another embryo. 

 Plate 11, Fig. I — Zonitoides arboreus Say, quite young, anterior part; 



x 600. 

 II — The same, nearly mature; x ca. 750. 

 Ill — Zonitoides ligerus Say, young, 3 mm. diam. ; x 400. 

 IV — The same, adult, 9 - 5 mm. diam. ; x 400. 

 V — Polygyra tridentata Say, young, mm. diam.; x 400. 

 VI — The same, adult, 15 mm. diam. ; x 400. 

 VII — Patula striatella Anth., adult, 5*3 mm. diam.; 



x 470. 

 VIII — The same, embryo, 1 *0 mm. diam. ; x 400. 

 IX — The same, very young embryo, buccal body, 0*12 

 mm. diam. 



