Uniicrsity of Michigan 



PLATE I 



The magnification of each of the figures is indicated by the hair- 

 line under it; this represents an actual length of 50 microns (.05 mm.). 



Figure i. Drymccus albostviatus. The central and the tips of the 

 first laterals. The ist, 3rd, 28th, looth and I35th (outermost) teeth 

 on the right side. The ^'-line shows the arrangement of a transverse 

 row. 



Figure 2. Dryiiiaus domiiiicus. Same arrangement as Figure I. 

 The tip of a tricuspid central (from another radula) is shown between 

 the central and the first lateral. 



Figure 3. Buliiitiilus coriaccus. Central and ist, 3rd, 7th, 14th 

 and 21 St teeth on right side. 



Figure 4. Oxystyla priiiccps. Aculeate type ui laterals irDUi a 

 single longitudinal row, to show the efifects of wear. The 2nd left 

 lateral of the 2nd, 7th, 14th, 35th, 49th, 56th and 77th transverse rows, 

 counting from the anterior end of the radula. 



Figure 5. Drymccus iinilliliiieutiis. Same arrangement as Figure i. 



Figure 6. Opcas bcckianum. The central, the ist, 7th, I4lh, 20th 

 and 2ist (outermost) teeth of the right side. 



