G. E. Beecher — Development of the Brachiojpoda. 357 



Figure 9. — Ventral protegulum of same species similarly modified, agreeing 

 with figure 7. x 25. 



Figure 10. — Lower valve of same species; showing submarginal position of 

 pedicle opening. Natural size. Recent. Callao, Peru. 



Figure 11. — Lower valve of Schizotreta tenuilamellata, Hall; showing centripetal 

 tendency of pedicle opening. Natural size. 



Niagara Group. Hamilton, Ontario. 

 (Pal. N. Y. Extract from vol. viii, pi. IVe, fig. 10, 1890.) 



Figure 12. — Lower valve of Acrothele subsidua (after Linnarsson); showing sub- 

 central position of pedicle opening. Natural size. 



Protremata. 



Figure 13. — Dorsal protegulum and early nepionic growth lines of Plectambonites 

 segmentina, Angelin. x 80. Upper Silurian. Gothland, Sweden. 



Figure 14. — Dorsal protegulum of Ghonetes scitulus, Hall, x 80. 

 Hamilton Group. Thedford, Ontario. 



Figure 15. — Accelerated discinoid ventral protegulum of Ghonetes granuliferus, 

 Owen ; showing pedicle notch, x 80. 

 Coal Measures. Manhattan, Kansas. 



Figure 16. — Discinoid nepionic stages of ventral valve of Orthotetes elegans, 

 Bouch. x 25. Compare with figure 12 of Acrothele. 

 Devonian. Ferques, France. 



Figure 17. — Nepionic stages of Stropheodonta perplana, Conrad; showing pedicle 

 perforation, pseudo-deltidium, and hinge area, x 25. 

 Hamilton Group. Falls of the Ohio. 



Figure 18. — Ventral nepionic discinoid stage of Strophomena rhomboidalis, "Wilck. 

 x25. 



Figure 19. — Profile of the same, x 25. 



Lower Helderberg Group. Albany County, New York. 



Figure 20. — Hinge of a specimen 2 mm in length ; showing deltidial covering and 

 hinge area. 



Figure 21. — Ventral view of specimen having same dimensions; showing nepi- 

 onic and nealogic stages, and relative proportions of pedicle open- 

 ing and shell at this stage. Niagara Group. Waldron, Indiana. 

 Figures 20 and 21 are taken from "Development of Some Silurian 

 Brachiopoda," Mem. N. Y. State Museum, vol. i, No. 1, pi. II, 

 figs. 2, 12, 1889. 



Telotremata. 



Figure 22. — Ventral view of young Kraussina (Megerlina) Lamar ckiana, David- 

 son ; showing protegulum and early nepionic stages, x 80. 

 Figure 23. — Dorsal view of same ; showing dorsal protegulum and pedicle open- 

 ing in ventral valve. x 80. Recent. Port Jackson, Australia. 

 Figure 24. — Dorsal view of beaks of young Terebratulina septentrionalis, Cou- 

 thouy ; showing dorsal protegulum and pedicle opening in ventral 

 valve, x 80. Recent. Eastport, Maine. 

 Figures 25-28. — Diagrammatic representation of ventral areas; showing pro- 

 gressive development of deltidial plates. Figure 25 is with- 

 out plates, as in ventral area of figure 23. Figure 26 shows 

 two triangular plates, which unite by symphysis in figure 27, 

 making an elongate pedicle opening. In figure 28, pedicle 

 perforation is subcircular and truncates ventral beak. This 

 series corresponds essentially with that shown in Rhyncho- 

 treta cuneata, Dal., in " Development of Some Silurian Brachi- 

 opoda," loc. cit., pi. IV, figs. 16-22. 



