14 Traris. Acad. Sci. of St. Louis. 



Suborder Stylommatophora. 

 HETERUEETHRA. 



Family Succineidae. 



SucciNEA RETUSA Lea. 



Sulphur Island; Sugar Island (large); Thunder Bay 

 Island (small); Ox Bow. 



Retusa varies much in the acuteness of its spire. Speci- 

 mens from Ox Bow are white in color and very transparent. 

 It is frequently identified as higgiusi. 



SucciNEA AVARA Say. 



Considerable variation is exhibited by this species in the 

 matter of size and shape. The following variations occur: 



Sulphur Island. Small, long and narrow- 8 mill. 



Thunder Bay. Small, with short spire and wide body 

 whorl 7 mill. 



Sugar Island. Large and small specimens mixed. 



Ox Bow. Very large, rather narrow. 12 mill. 



Isaacson's farm. One specimen. 



Family Helicidae. 



POLYGYRA ALBOLABRIS Say. 



Sulphur Island ; Thunder Bay Island ; Alpena. 



Some specimens are rather depressed and very thin. One 

 specimen is provided with two projecting, triangular, tooth- 

 like processes, caused by the repairing of a break in the shell; 

 one is over the periphery and projects about two millimeters. 



POLYGYRA MONODON Rackett. 



Sugar Island. Common. 



POLYGYRA MONODON FRATERNA Say. 



Alpena; Sulphur Island ; Thunder Bay Island. Common. 

 Family Zonitidae. 



EucoNULUS ruLvus Miiller. 



Thunder Bay Island; Sugar Island. Typical. 



