THE MOLLUSC A OF GEORGIAN BAY 107 



SESSIONAL PAPER No. 39b 



Sphaerium {Musculium) securis, Prime. Abundant in sandy channels. Small, 

 fragile, much higher in front of umbones which are centrally placed. Truncated 

 behind, rounded in front, rhomboidal in outline, umbones calyculate and inflated, 

 marked by fine concentric lines; lines of growth fine. Found in stomachs of white- 

 fish. (PI. X, Fig. 13). 



Sphaerium (Musculium) partumeium, Say. Identified by Mr. E. G. Vanatta. 

 Sand channels. Shell equilateral, oval in outline, large, truncated behind, color 

 yellow, lines of growth fine. 



Genus Pisidium. 



One species of this genus occurs here. 



Pisidium virginicum, Bourguignat. Abundant in sandy channels. Dark 

 colored. Umbones elevated, placed posteriorly, shell heavy, brown or yellowish, 

 truncated behind, triangular in front. Lines of growth coarse. Cardinal teeth 

 single in right valve, inverted V-shaped; double in left; oblique, anterior narrow, 

 posterior stout, inclined tow^ards pyramidal. Laterals stout, double in right valve, 

 single in left. 



ARTIFICIAL KEY TO THE SPECIES IN THIS REPORT. 



Since the recognition of these species is not an easy matter the following key 

 based upon shell characters is given to facilitate their identification. 

 A. 1. Univalve, shell consisting of one valve. 



B. 1. Non-operculate, no operculum borne on upper surface of foot and 

 closing the aperture of shell when animal is retraced. 

 C. 1. Spire elevated and dextral, or flat. 

 Family lymnaeidae. 

 D. 1. Spire elevated and dextral. 

 Genus Lymnaea. 

 E. 1. Spire elongated. 



F. 1. Much elongated and slender, whorls very oblique, shell thin. 



Lymnaea haldemani. 

 F. 2. Elongated but stout; dark colored. 

 Lymnaea palustris. 

 E. 2. Spire short. 



F. 3. Thin-shelled, body whorl very large, whorls very oblique. 

 Length of shell 15-18 mm. 

 Lymnaea columella. 

 F. 4. Shell large, smooth; whorls 5; length of shell 25-30 mm. 



Lymnaea stagnalis sanctaemarioe. 

 F. 5. Shell medium sized, usually malleated; whorls 5; length of 

 shell 20-25 mm. 

 Lymnaea emarginata candensis. 

 F. 6 — Shell small, smooth; whorls 3; length of shell 10-12 mm. 

 Lymnaea decollata. 



