Plate I. 



Vol. Ill 



Helix arbtistorum L. — i Jaw; 2, 3, 4, other examples. 5, Teeth. 6, a. Dart, 

 x6; h, transverse mid-section of head. 7, Dissection of dart-sac, before form- 

 ation of dart. 8, Dart-sac after shedding dart. 9, Comis Brazieri G .'&. Sow- 

 erby, junr. 



