176 A NATURALIST IN THE GREAT LAKES REGION 



left-handed coil of its shell and the fact that the aperture is less 

 than two-thirds the length of the shell, Lymnaea reflexa and 

 Planorbis bicarinatus (Fig. 324) the former more abundant in the 

 older ponds. Lymnaea humilis and L. desidiosa are pretty much 

 confined to the younger ponds. Planorbis parvus, P. campanu- 

 latus, P. hirsutus are occasionally found in all the relatively newer 



FIG. 193. Brown or spotted bullhead, Ameiurus nebulosus. After Forbes 



ponds. Snails of the genus Amnicola have small (.3 inch or 

 less) conical shells, the mouth of which is closed when the animal 

 draws back into its shell by a horny close-fitting disk, the oper- 

 culum. The edge of the opening is not connected with the body 





FIG. 194. Tadpole cat, Schilbeodes gyrinus 



of the shell. In A. cincinnatiensis the aperture of the shell is 

 nearly half as wide as the shell is long. In A . limosa the round 

 opening is pressed quite against the body of the shell which is 

 unusual in the genus. The Lymnaeas do not have an oper- 

 culum. The shell is long with six or so whorls. L. reflexa is 

 .8 to 1.6 inches long. The spire is longer than the aperture. 

 The edge of the aperture is strongly turned back. L. humilis and 



