512 THE CHICAGO ACADEMY OF SCIENCES. 



inner cusp ; 5, mesocone or middle cusp ; 6, ectocone or outer 

 cusp. X 516. 



D. First lateral and a marginal (13) tooth of Galba reftexa, to show 



appearance when worn by use. X 516. 



E. Sculpture of Lymncea consisting only of growth lines. (X 50.) 



F. Sculpture of Lymncea showing the breaking up of the rib-like growth 



lines to form pseudo-spiral lines. (X 50.) 



G. Galba reftexa (SAY), showing position of openings into body. 1. 



respiratory opening; 2, anus; 3, orifice to female organs; 4, ori 



fice of male organ. 



H. Animal of Galba obrussa (SAY), from above. 

 I. Animal of Galba emarginata mighelsi (BINNEY), from the side. 

 J. The same, from below. 

 K. The same, from above. 1, eye; 2, tentacle; 3, velum; 4, foot; 5, 



respiratory siphon; 6, edge of mantle forming the collar, which 



closely embraces the outer and inner lips. 



PLATE IV. 



Figure A. Galba pilsbryi (HEMPHILL). Type, drawn by H. A. Pilsbry. En- 

 larged. 



B. Galba pilsbryi (HEMPHILL). Side view of last whorl. Drawn by 



H. A. Pilsbry. Enlarged. 



C. Galba bakeri (WALKER). Type, drawn by Bryant Walker. Enlarged. 



D. Innervation of female organs of Lymncea (after Lacaze-Duthiers). 



1, oviduct; 2, penis; 3, duct of receptaculum seminis; 4, nerve; 

 5, anterior pallial nerve; 6, right pallial nerve. 



E. Egg capsule of Lymnoea. (X 8.) 



F. Retractor muscles of Galba renexa. 1, buecal sac; 2, right and left 



retractors of buccal sac; 3, penis-sac retractor; 4, penis re- 

 tractor; 5, muscles protracting and depressing the buccal sac. 

 (Greatly enlarged.) 



G. Male organs of Lymncea. 1, penis partly everted in penis-sac; 2, 



penis fully inverted; p, penis; ps, penis-sac; vd, vas deferens. 



Note the different shape of the penis-sac in the two conditions. 

 H. Cross sections of penis of Galba reflcxa (SAY), to show the longitudi- 

 nal internal folding. The particular position of each section is 



indicated on the outline to the left. 

 I. Comparisons of the length of the penis and the penis-sac in four 



species of Lymncea. 1, stagnalis; 2, emarginata; 3, palustris; 



4, auricularia. 

 J. Penis of Lymncea stagnalis lilliance, as it appears in life during the 



breeding season ( August). 1, front view; 2, side view. 



PLATE V. 



NERVOUS SYSTEM. 1 



Viewed from above; only the right tentacle and left large labial nerves are 

 shown: 1, cerebral ganglia; 2, pleural ganglion of right side; 3, visceral gan- 



*In the preparation of the nervous system of Galba reflexa, Lacaze-Du- 

 thiers' figure (pi. 17, fig. 2) in Archiv. Zool. Exp., has been closely followed as a 

 guide, and the figure here presented differs little from the one in the work 

 mentioned. 



