PLATE VI 



SpIRIFER BICOSTATUS, var. PETILUS, Hall 



P»Ke 75 

 Pigs. 1, ta. The younf(est example observed, and outline profile of the same. 

 Fig. a. Dorsal view of a large specimen. 

 Fig. y Cardinal view of the same, x 3, (nth Rept. State Geol. Ind., pi. 37, figs. 8, 9.) 



SpiRIFER CRISPUS, var. SIMPLEX, Hall 



Page 75 

 Fig. 4. Dorsal view of the youngest growth-stage observed. Within the single growth-line, the smooth subcircular initial shell 



is visible, but outside this, the shell has developed the median fold and the surface fimbriae. 

 Fig: 4/>. Outline profile of the same. 

 Fig. 5. Dorsal view of a mature individual, X2. 

 Fig. 6. Profile of the same. (38th Ann. Kept. N. Y. State Mua. Nat. Hist., pi. 34, figs, i, 4.) 



Spirifer CRISPUS, Hisinger 



Page 75 

 Fig. 6. Dorsal view of a young form, in which the deltidial plates are in an incipient condition. 

 Fig. •6(1. Outline profile of the same. 

 Fig. 7. Dorsal view of a mature specimen. 

 Fig. 7a. Profile of the same. (28th Ann. Rept. N. Y. Sute Mus, Nat. Hist., pi. 34, figs. 8, is.) 



Spirifer niagarensis, Hall 



Page 80 

 Fig. 8. The cardinal area of a ventral valve, from Lockport, New York. The deltidial plates are in the third static of develop- 

 menL the foramen nOt yet inclosed but conDueQt with the hiattis bclov^ ttie basal edge! of the plateaL Natural size. 



Spirifer radiatus, Sowerby 



Page 77 

 Fig. 9. A cardinal view; showing a similar stage of development of the deltidium; from an individual which has not attained 



normal full-growth. 

 Fig. 10. The youngest growth-stage observed. 

 Fig. loa. Outline profile of the same. 

 Fig. n. Dorsal view of a normal adult. 

 Fig. tta. Profile of the same. (28th Ann. Rept. N. V. State Mus. Nat. Hist., pi. 24, figs. 33,35.) 



Atrypa reticularis, Linnaeus 



Page 51 



Fig. 12. The incipient shell, having a length of 2.25 mm. The deltidial plates have already begun to form, and the shell has de- 

 veloped two growth-lines. 



Fig. i2d. Outline profile of the same. 



Fig. 13. Ventral view of a tull-grown individual. 



Fig. ijrt. Profile of the same. (23th Ann. Rept. N. Y. State Mus. Nat. Hist., pi. 25, figs. 46, 47.) 



Fig. 14. A scries of outlines of the anterior margin of the valves; showing the rapid increase in plications and the reversion from 

 the embryo fold and sinus to the sinus and fold of maturit)'. 



Fig. 15. The deltidial characters of the specimen represented in figure 12. 



Fig. 15a. Outline profile of the same. 



Fig. 16- Similar view of a specimen measuring 3x3 mm. 



Fig. ita. Outline profile of the same. 



Fig. 17. Similar view of a specimen measuring 3.5x4 mm. 



Fig. 17a. Outline profile of the same. 



Fig. 18. Similar view of a specimen measuring 8x7 mm. 



Fig. i8<i. Outline profile of the same. 



Fig. 19. Similar view of a specimen measuring 21 x3o mm. 



Fig. X9a. Outline profile of the same. 



Fig. ao. Similar view of a full-grown specimen measuring 34 k aa mm. 



Fig. 9(M. Outline profile of the same. 



