7<S Bcechci' and SrJi tir]ierl — Braclihil Supports. 



Figure 11.— A little more advanced .stase, Hliowing increased length of 

 connecting band. X 12. Specimens figures 7-11 are from 

 the Trenton shales, St. Pmd, Minnesota. 



12. — A looped s1,age, with l)road, curved, dsscending 1)ranches and 

 more slender transverse band. X 6- 



13. — The same ; profile. X 6- 



14.— A later stage, showing more slender loop. X (i. 



15. — A specimen showing curved, diverging, descending ])ranches, 

 long transverse band, and two projections of the lamella', 

 M'hich are the beginning of the spiral cones. X '>- 



16.— A subsequent stage in which the lamelUie are more extended 

 and ventrally and inwarrlly curved. X ()• 



17. —The same ; pi'ofile. X <>• 



18. — A young individual in which there are about one and one- 

 half turns to each spiral. X (>. 



19. — The same ; profile- X <>. 



20 — The bracliial supports in a mature specimen. X (i. Tlie 

 specimens figures 12-20 are from the top of tlie Trenton, 

 Frankfort, Kentuch/. 



21. — The spirals and loop in a Canadian specimen of {Anazi/(/a -) 

 Zi/(/osplru rccnrrlrostra. (After Davidson.) X 3. 



22. — Tlie spirals and loop in {IlaUina =) Z[/(/ospir(( .sajfurili W. and 



S. Trenton, Tennessee. X 6. 

 1 2o. — The spirals and loop in {HaUina ==) Zygosplra nlculJctti W. and 



S. Trenton, 3finnesota. X 0. 

 24. — The spirals and loop in Zijgonpira Iwad'i Billings. (After 



Hall.) X 2. 

 25. — The spirals and loop in Zyt/ospira modesta Say. (After Hall.) 



X 2i. 

 2().— The same. (After Davidson.) X :'.'.. 



