BAKER: FIELDBOOK OF ILLINOIS LAND SNAILS 7 



co72cavum, shown in fig. 6. This snail has but 51 teeth in a row 

 and only S2 rows, 1,632 teeth in all. 



Though the teeth of snails furnish evidence on which 

 species may be separated, our purpose in this fieldbook is not 



Fig. 3. — Two rows of teeth from the left side of a radula membrane 

 of Po/ygyra tridentata (Say). 



Reflected Portion 

 Side Cusps 



Cutting Point 

 Middle Cusp 

 Cutting Point 



Cutting Point 



Base of 

 attachment 



Lateral TcotTT ^° ^^^-^^^ 



Base of 

 attachment 

 to raoula 



-Cutting 

 Point 



Median Tooth Marginal Tooth 



Fig. 4. — The three kinds of teeth, lateral, median and marginal, on 

 the radula or lingual ribbon of a land snail, greatly magnified. 



Fig. 5. — Longitudinal section of the radula of a land snail. The 

 teeth lie on the radula membrane much as shingles lie on a roof. 



&/^^^^ 



Fig. 6. — Teeth from the radula or lingual ribbon of the carnivorous 

 snail Haplotrema concavum (Say). 



to discuss the subject of finer anatomy. Instead, our object is 

 to point out the readily observable means of recognizing the 

 shells of Illinois land snails. 



Food of snails. — The great majority of snails feed upon 

 vegetable matter. Thistles, nettles, fungi, succulent leaves and 



