Fig. 15. An enlargement from the central portion of a segment. x6. 



Fig. 16. An enlargement from another segment, showing angular form 

 and median carination. x6. • 



Fig. 17. An enlargement from the base of a segment. x6. 



Figs. 18-20. Transverse sections from different portions of a seg- 

 ment. x6. 

 Hamilton group. New York, 



649 



