PLATE XX 



RETICULARIA BICOSTATA, VAR. PETILA HALL (PAGES 380-382) 



FIGURES 1, la. The youngest example observed, and outline profile 

 of the same. 



FIGURE 2. Dorsal view of a large specimen. 



FIGURE 3. Cardinal view of the same. X 3. (\\thRept. State Geol. 

 Ind., pi. 27, figs. 8, 9.) 



SPIRIFER CTRSPUS, VAR. SIMPLEX HALL (PAGES 380-382) 



FIGURE 4.- Dorsal view of the youngest growth-stage observed. 

 Within the single growth-line, the smooth sub-circular initial shell is 

 visible, but outside this the shell has developed the median fold and the 

 surface fimbriae. 



FIGURE 4a. Outline profile of the same. 



FIGURE 5. Dorsal view of a mature individual. X 2. 



FIGURE 5a. Profile of the same. (2Sth Ann. Rept. N. Y. State Mus. 

 Nat. Hist., pi. 24, figs. 1, 4.) 



SPIRIFER CRISPUS HISINGER (PAGES 380-382) 



FIGURE 6. Dorsal view of a young form, in which the deltidial 

 plates are in an incipient condition. 



FIGURE 6a. Outline profile of the same. 



FIGURE 7. Dorsal view of a mature specimen. 



FIGURE la. Profile of the same. (2Sth Ann. Rept. N. Y. State Mus. 

 Nat.- Hist., pi. 24, figs. 8, 12.) 



SPIRIFER NIAGARENSIS CONRAD (PAGE 385) 



FIGURE 8. The cardinal area of a ventral valve, from Lockport, 

 New York. The deltidial plates are in the third stage of development ; 

 the foramen not yet enclosed, but confluent with the hiatus below the 

 basal edges of the plates. Natural size. 



