PLATE XXIII. 



Platyceras dumosum. 



Fig. 1-4. A series of specimen showing variations in size, distribu- 

 tion and condition of spines. Page 162 

 Fig. 5, 6. View of two specimen exfoliated, and showing spine bases. 

 Fig. 12. Vertical view of a young specimen. 



Platyceras dumosum, var. rarispinum. 



Fig. 7, 8. Dorsal and lateral view of a specimen. Page 163 



Platyceras bucculentunu 



Fig. 9, 11. Lateral view of two specimen, showing variation in size. Page 160 



Platyceras symmetricum. 

 Fig. 10. Lateral view of a specimen. Page 167 



