PLATE III 



STROPHONELLA STRIATA, Hall 



Page 25 

 Fig. i. Ventral view of the incipient shell of the series (length 2.25 mm.): showing the opening of the pedicle-sheath, and the 



primary surface plications 

 Fig. Irt. Outline profile of the same; showing the complete convexity of the ventral valve, and essentially conformable concavity 



of the dorsal valve. 

 Fig. 2. Ventral valve of a normal adult; showing the umbonal convexity of the shell and general concavity over the pallial 



region. (28th Rept. N. Y. State Mus. Nat. Hist., pi. 23, fig. i.) 



Fig. 2. Outline profile of the same; showing the reversal in convexity from the embryo condition. 

 Fig. 3. Pedicle-area of the specimen represented in fig. i (length 2.25 mm.); showing the well-developed, slightly cxsert sheath 



and the obscure dorsal callosity. 



Fig. 4. Pedicle-area of an individual, 2.5 mm. in length, in which the sheath is extravagantly exsert. 

 Fig. 5. Pedicle-area in an example about 6 mm. in length. 

 Fig. 6. Pedicle-area, when a length of 8 mm. has been attained. 

 Fig. 7. Pedicle-area in a shell measuring 13 mm. in length. 

 Fig. 8. Pedicle-area in a normal adult measuring 17 mm. in length. 



Figs. 3-8 have been drawn to the same scale, and show the successive phases in the development of the pedicle 

 characters. The sheath ceases its function as a pedicle-passage before maturity is attained, though retaining its 

 relative size, while the dorsal callosity, which in the earlier stages is grooved and largely enveloped by the sheath, 

 is eventually separated from the sheath by a narrow aperture, and its surface becomes uninterrupted. 



STREPTIS WALDRONENSIS, Miller and Dyer 



Page 30 



Fig. 9. Dorsal view of a young individual having a length of 3 ram. The shell is nearly symmetrical, and shows an open triangu- 

 lar deltidium, ending in a subcircular apical foramen. 

 Fig. ga. Ventral view of the same; showing the apical foramen. 

 Fig. g6. Outline profile of the same. 



Fig. io. Cardinal view of an adult specimen; showing the asymmetrical shell. 

 Fig. iort. Dorsal view of the same. 

 Fig. io. Ventral view of the same, (nth Ann. Rept. State Geol. Indiana, pi. 27, figs. 21, 19, 20.) 



ElCHWALDIA RETICULATA, Hall 



Page 31 



Fig. ii. A young individual having a length and width of 3 mm. ; showing the subcircular outline and undefined median fold. 

 Fig. 12. Axial section of a larger, but immature form; indicating the character of the articulation, and showing the internal ventral 



plate and dorsal septum 

 Fig. 13. Dorsal view of an adult shell, x 2. 



Fig. i3fl. Cardinal view of the same; showing the bare umbonal area and the lines of lateral attachment of the internal plate, x 2. 

 (Figs. 13, i3 from the 28th Rept. N. Y. State Mus. Nat. Hist., pi. 26, figs. 53, 54.) 



ANASTROPHIA INTERNASCENS, Hall 



Page 32 



Fig. 14. Ventral view of the youngest specimen observed (length 2 mm.). 



Fig. 14(1. Outline profile of the same; showing the elevation of the ventral beak and cardinal area. 

 Fig. 15. Dorsal view of a large adult. 



Fig. 16. Ventral view of an average adult; showing the overlapping dorsal valve. 

 Fig. i6a. Profile of the same; showing the relative convexity of the valves. 



(Figs. i5-i6 from the 28th Rept. N. Y. State Mus. Nat. Hist., pi. 26, figs. 49, 45, 44.) 



RHYNCHONELLA INDIANENSIS, Hall 



Page 42 



iid v c <i[j|^rt.i <ju, a. i in LUO uuugiua ui LUC luiitiiicu iitivc ucuuuii; LIIR tvunuti. 

 Fig. i8rt. Outline profile of the same. 



Fig. 19. A young example with a length of 6 mm.; showing the inception of the median fold, (nth Ann. Rept. Geol. Surv. Ind., 

 pi. 27, fig. 6.) 



pi. 27, fig. 6.) 

 Fig. 20. Dorsal view of a larger example, natural size, having two plications on the fold, and abnormal in the absence of all lateral 



plications (op. cit.^ fig. 5). 



Fig. 21. Dorsal view of a small, essentially mature example, with two plications on the fold (op. cit.^ fig. 4). 

 Fig. 22. Dorsal view of anadult with three plications on the fold. (a8th Rept. N. Y. State Mus. Nat. Hist., pi. 26, fig. 13.) 

 Fig. 23. Front view of an adult with four plications on the fold (op. cit.^ fig. 22). 

 Fig. 24. Dorsal view of a similar individual . 

 Fig. 24^. Profile of the same (op. cit., figs. 15, 19). 

 Fig. 25. An enlargement of the cardinal area in an individual with a length of 1.5 mm.; showing essentially the primitive charac- 



ters seen in fig. 17. 



Fig. 250. Outline profile of the same. - 

 Fig. 26. The condition of the ventral cardinal area and foramen in an individual 3.5 mm. in length. The margins of the foramen 



are thickened by the inception of the deltidial plates and the aperture is seen to encroach upon the apical portion of the 



shell. 



hiefly in rapid development 

 incurved umbo. 



. 



Fig. 26*7. Outline profile of the same. 

 Fig. 37. The cardinal features in an individual of 7 mm. length. The advance upon the last stage is chiefl 



of the deltidial plates, which have narrowed the opening, slightly constricting it near the now ncurve umo. 

 Fig. 2ja. Outline profile of the same. 

 Fig. 28. The cardinal features in an adult, having a length of io mm. The deltidial plates have united at their base, forming an 



elongate oval aperture, encroaching upon the umbo. The species does not pass this stage of development. 

 Fig. ySa. Outline profile of the same. 



