NATURAL SCIENCES OF PHILADELPHIA. 239 



Plate X. 



Fig. 1. Helix tridentata, Say. 

 Fig. 2. Helix palliata, Say. 



a. Central and first lateral. 



b. An outer lateral. 



c. A transition tooth between laterals and marginals. 



d. A marginal tooth. 

 Fig. 3. Helix Rugeli, Shuttl. 

 Fig. 4. Helix inflecta, Say. 

 Fig. 5. Helix fallax, Say. 



Fig. 6. Helix Hopetonensis, Shuttl. 



b. Marginal teeth. 

 Fig. 7. Helix appressa, Say. 



Plate XI. 



a. Central and lateral. 

 6. Inner marginal. 



c. Outer marginal. 



d. Transition from lateral to marginal. 

 Fig. 1. Helix albolabris, Say. 



Fig. 2. Helix Wetherbyi, Bl. 

 Fig. 3. Helix Roemeri, Pfr. 

 Fig. 4. Helix Downieana, Bl. 

 Fig. 5. Helix Sayii, Binn. 

 Fig. 6. Helix Clarki, Lea. 

 Fig. 7. Helix exoleta, Binn. 



Plate XII. 



Fig. 1. Helix elevata, Say. 

 Fig. 2. Helix Columbiana, Lea. 

 Fig. 3. Helix Mobiliana, Lea. 



b. Extreme marginals. 

 Fig. 4. Helix devia, Gld. 



a. Central and lateral tooth. 



b. An extreme lateral. 



c. Marginal teeth. 



d. The last marginal. 

 Fig. 5. Helix profunda, Say. 

 Fig. 6. Helix multilineata, Say. 



