EXPLANATION OF PLATES 209 



Hyolithellus micans Billings 

 p. 38 



Fig. 



11 Internal cast of operculum, x 20 

 Pebble of group 1 



Hyolithus rhine sp. rvov. 

 p. 36 



12 Dorsal view of specimen. Natural size 



13 Lateral view of same. Natural size 



14 Enlargement of distal part of upper side, x 2 



15 Section of shell, x 2 

 Pebble of group 6 



