516 THE CHICAGO ACADEMY OF SCIENCES. 



PLATE XIII. 



Figure A. Genitalia of Planorbis trivolvis SAY. 1, penis; 2, penis appendage; 

 3, vas deferens ; 4, duct (portion of vas deferens) from penis 

 appendage; 5, nerve to penis appendage; 6, protractor muscles 

 of penis; 7, retractor muscles of penis; 8, left retractor of buc- 

 cal sac ; 9, duct from prostate ; 10, duct of receptaculum seminis ; 

 11, receptaculum seminis; 12, oviduct; 13, prostate; 14, ovisperm 

 duct; 15, ovotestis (the albuminiparous gland is omitted from 

 this figure). 



B. Radula of Planorbis trivolvis SAY. 1, central tooth ; 2, lateral tooth ; 



3, marginal tooth. 



C. Genitalia of Galba danielsi (BAKER). (Animal killed in Septem- 



ber.) 



D. Genitalia of Galba caperata (SAY). 



PLATE XIV. 



Variation in retractor and protractor muscles of male organ in Lymnsea. 

 Figure A. Lymncea stagnalis appressa SAY. M, transverse muscles. 



B. Lymncea stagnalis sanctcemaria WALKER. From Siskowit Bay, Isle 



Royale. 



C. Pseudosuccinea columella (SAY). 1-3, from Sea Breeze, near 



Rochester, N. Y.; 4, from La Porte, Ind. 



D. Bulminea megasoma (SAY). 1, one penis-sac retractor; 2, two re- 



tractors of penis-sac ; pr, penis retractor ; psr, penis-sac re- 

 tractor; ps, penis-sac; psp, posterior penis-sac protractors; psp 1 , 

 anterior penis-sac protractors. 



E. Galba parva (LEA). 



F. Galba umbilicata (ADAMS). Cayuga Lake, N. Y. 



G. Galba obrussa (SAY). 1, Sea Breeze, N. Y.; 2, Cayuga Lake, N. Y. 

 G, 3. Galba obrussa peninsulace (WALKER). 



PLATE XV. 



Variation in muscles of male organ. 

 Figure A. Galba rettexa (SAY). La Porte, Indiana. 



B. Galba emarginata (SAY). From Isle Royale specimens. 



C. Galba palustris (MULLER). Colorado specimens, ap, anterior penis- 



sac protractors; cm, columellar muscle; pp, posterior penis-sac 

 protractors; pr, penis retractor; psr, penis-sac retractor. 



D. Galba reftexa (SAY). Calumet Lake, Illinois. 



E. Acella haldemani ((DESK.) BINNEY.) 



F. Galba catascopium adamsi BAKER. 1-3, St. Clair flats, Mich. 



F. Galba catascopium (SAY). 4-6, Erie Canal, Rochester, N. Y. ; 7-8, 



Genesee River, Rochester, N. Y. 



G. Galba elodes jolietensis (BAKER). 



PLATE XVI. 



FOSSIL LYMN^AS. 



Figure 1. Lymncea ativuncula WHITE. Bull. U. S. Geol. Surv., No. 29, pi. 4, 

 fig. 10. Type. 



