PLATE VI 



SPIRIFER BICOSTATUS, var. PETILUS, Hall 



Page 75 



Figs, i, irt. The youngest example observed, and outline profile of the same. 

 Fig. 2. Dorsal view of a large specimen. 

 Fig. 3. Cardinal view of the same, *$. (nth Rept. State Geol. Irid., pi. 27, 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. 4rt. Outline profile of the same. 



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

 Fig. 6. Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pi. 24, 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. 6rt. Outline profile of the same. 

 Fig. 7. Dorsal view of a mature specimen. 

 Fig. ^a. Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pi. 24, figs. 8, 12.) 



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 stage of develop- 

 ment, the foramen not yet inclosed but confluent with the hiatus below the basal edges of the plates. 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. ioa. Outline profile of the same. 

 Fig. ii. Dorsal view of a normal adult. 

 Fig. iirt. Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pi. 24, figs. 23, 25.) 



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. i2a. Outline profile of the same. 



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



Fig. 13/1. Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist, pi. 25, figs. 46, 47.) 



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

 the embryo fold and sinus to the sinus and fold of maturity. 



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



Fig. i5rt. Outline profile of the same. 



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



Fig. i6rt. Outline profile of the same. 



Fig. 17. Similar view of a specimen measuring 3.5 X4 mm. 



Fig. 17*1. Outline profile of the same. 



Fig. 18. Similar view of a specimen measuring8x7 mm. 



Fig. i8. Outline profile of the same. 



Fig. 19. Similar view of a specimen measuring 21 x 20 mm. 



Fig. 19**. Outline profile of the same. 



Fig. 20. Similar view of a full-grown specimen measuring 24 x 22 mm. 



Fig. zotf. Outline profile of the same. 



