PLATE XX 



RETICULARIA BICOSTATA, var. PETILA Hall (Pagks 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. {\\l/i Rept. Stale Geol. 

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



SITRIFER CIRSPUS, var. SIMPLEX Hall (Pages 380-382) 



Figure 4. — Dorsal view of the youngest growtli-stage observed. 

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

 visible, but outside this the shell has developed the median I'old and tlie 

 surface fimbria^. 



Figure 4a. — Outline profile of the same. 



Figure 5. — Dorsal view of a mature individual. X 2. 



Figure or/. — Profile of the same. (2Sth Ann. Repl. N. Y. Slate Mas. 

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



SPIRIFER CRISPUS Hisinger (Pages 380-382) 



Figure 6. — Dorsal view of a young form, in whicli tlie deltidial 

 plates are in an incipient condition. 



Figure 6a. — Outline profile of the same. 



Figure 7. — Dorsal view of a mature specimen. 



Figure 7o. — Profile of the same. (28^/i Ann. Repl. N. Y. Stale Mus. 

 Nat. HisL, pi. 24, figs. 8, 12.) 



SPIRIFER NIACtARENSIS Conrao (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. 



