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 reflexa, to show 
appearance when worn by use. X 516. 
E. Sculpture of Lymnea consisting only of growth lines. (X 50.) 
F. Sculpture of Lymnea showing the breaking up of the rib-like growth 
lines to form pseudo-spiral lines. (X 50.) 
G. Galba reflera (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 TY. 
Figure A. Galba pilsbryi (HEMPHILL). Type, drawn by H. A: Pilsbry. En- 
larged. 
B. Galba pilsbryt (Hempuitt). 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 Lymn@a (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 Lymnaea. (X 8.) 
F.- Retractor muscles of Galba reflexa. 1, buccal 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 Lymne@a. 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 refexa (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 Lymnea. 1, stagnalis; 2, emarginata; 3, palustris; 
4, auricularia. 
J. Penis of Lymnea stagnalis lilliane, as it appears in life during the 
breeding season( August). 1, front view; 2, side view. 
PLEAD E We 
NERVOUS SYSTEM.* 
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- 
1In the preparation of the nervous system of Galba reflexa, Lacaze-Du- 
thiers’ figure (pl. 17, fig. 2) in Archiv. Zool. Exp., has been closely followed asa 
guide, and the figure here presented differs little from the one in the work 
mentioned. 
