PLATE XXVI 

 DIELASMA TURGIDUM Hall (Pages 412, 4i;i) 



Figure 1. — The centrouelliform stage of the loop; ventral view. 

 X9. 



FiGUUK 2. — A later stage; showing the resorption of the anterior jior- 

 tion of the loop. X 6. 



FiGUKK 3. — Early Dielasma stage, produced by further resorption of 

 tlie ceiitronelloid loop. X 6. 



Figure 4. — Loop and crural plates of mature specimen, x 'J- 



FiGUKK .5. — Prolile of the connecting band. X 6. 



Figure (i. — Side view of the loop, crnra, and septum, x 6. 



St. Louis Group, Kentucky. 



ZYGOSPIRA RECURVIROSTRIS Hall (Pages 413-416) 



Figure 7. — Centi-oneUiform stage of the looj>. x 12. 



Figure 8. — Profile of same. X 12. 



Figure i). — A later stage ; showing partial resorption of loop in 

 front and greater divergence of descending branches. X 12. 



Figure 10. — The same ; prolile. X 12. 



Figure 11. — A little more advanced stage ; showing increased lengtli 

 of connecting band. X 12. 



Specimens figures 7-11 are from the Trenton Shales, St. Paid, 

 Minnesota. 



Figure 12. — A looped stage, with broad, curved, descending branches 

 and more slender transverse band. X 6. 



Figure 13. — The same; profile. X 6. 



Figure 14. — A later stage; showing more slender loop. X G. 



Figure 15. — A specimen showing curved, diverging, descending 

 branches, long transverse band, and two projections of the lamelL-e, which 

 are the beginning of the spiral cones. X 6. 



Figure 16. — A sub.sequent stage in which the lamellae are more ex- 

 tended and ventrally and inwardly curved. X 6. 



Figure 17. — The same ; profile. X 6. 



FiGUi{E IS. — A young individual in which there are about one and 

 one-half turns to each spiral. X 6. 



Figure 1J>. — TIh; same; profile, x 6. 



Figure 20. — The brachial sujiports in a mature specimen. X 6. 



The sjiecimens figures 12-20 are from the top of the Trenton, Frank- 

 fort, Kentucky. 



Figure 21. — The spirals and loop in a Canadian specimen of {Ana- 

 zyr/nz=) Zi/fjospirn recurriroMris Hall. (After Davidson.) X 3. 



Fi(;uKE 22. — The spirals and loo)i in {lldllina =) Zygospira Saffordi 

 Wiiichell and Schuchert. Trenton, Tennessee. X 6. 



Figure 23. — The spirals and loo]i in {IlaUina =) Zygospira Nicolletti 

 Winchell and Schuchert. Trenton, Minnesota. X 6. 



Figure 24. — The spirals and loop in Catazyga Heath Billings. 

 (After Hall.) x2. 



Figure 25. — The spirals and looji in Zygoapirn modesta Say. (After 

 Hall.) X 2^. 



Figure 26. — The same. (After Davidson.) X 3^. 



