272 The Molluscan Family Planorbidae 



PLATE 18 



Gyraulus and Arniiger 



1-5. Gyrauhis similaris (F. C. Baker). From Smartweed Lake, near Tolland, Colorado; 

 collected by Dr. Frank Smith. 



1. Genitalia dissected and organs separated. 



2. Distal end of genitalia showing arrangement of durt.'<. 



3. Penial complex in section showing verge, stylet, and preputium. 



4. Stjdet. Outlet of sperm canal is shown at side of verge. 



5. Head and foot of animal showing pseiidobranch. 



6-11. Armiger crista (Linn.). From pond in Krolikarnia, a suburb of Warsaw, Poland; 

 collected by A. Jankowski. 



6. Head showing form of pseudobranch. 



7. Genitalia dissected and organs separated. 



8. Albumen gland from side. 



9. Penial complex in .section showing verge without stylet. 



10. End of verge showing absence of stylet and jjresence of a fleshy papilla. 



Sperm canal with outlet in center of verge. 



11. End of verge from side showing relationship of jiapilla and canal. 



Line near figure usually indicates 1 mm. in length. Line at left of fig. 4 



measures one-fifth of 1 mm. Line in center of fig. 7 is also for 



fig. 8. Same line equals 0.5 mm. for fig. 9. 



Figures 10 and 11 are much enlarged. 



