PLATE III 



Strophonella striata, Hall 



PaRcas 



Ventral view of the incipient shell of the series (lenf^ 2.35 mm.}; showinj; the opening of the pedicle-sheath, and the 



primary surface plications 

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



of the dorsal valve. 

 Ventral valve of a nonnal adult; showinc the umbonal convexity of the shell and general concavity over the pallial 



region. (28th Kept. N. Y. Stale Mus. Nat. Hist., pi. 23, fie. 1.) 

 Outline protile of the same; showing the reversal in convexity irora the embryo condition. 

 Pe<licle-area of the specimen represented in fig. i (length 2.35 mm.); showing the well-developed, slightly cxsert sheath 



and the obscure dorsal callosity. 

 Pcdicle-arca of an individual, 3 5 mm. in length, in which the sheath is extravagantly exsert. 

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

 Petiiclc-area, when a length of 8 mm. has been attained. 



Pedicle-area in a shell measuring 13 mm. in length. ^ 



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, 

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



Strkptis waldronensis, Miller and Dyer 



Page 30 

 Fiff. 9. Dorsal view of a young individual having a length of 3 mm. 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. 9^. Outline profile of the same. 



Fig. 10. Cardinal view of an adult specimen; showing the asymmetrical shell. 

 Fig. lod. Dorsal view of the same. 

 Fig. 10^. 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. 13. Axial section of a larger, but immature ^orm; iti()icatinc; the character'of Ihe articuUtio^, and fihoWiAjif'the ^iternai ventral 



plate and dorsal septum   . .  J -'^ . f . i i '- 



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



Fig. 13a. Cardinal view of the same; showing the bare umbonal area and the lines of lateral attachment of the internal plate, x 3. 

 (Figs. 13, i3rt from thq 28th Rept. N. Y. State Mus. Nat. Hist., pi. 26, figs. 53, 54.) 



Anastrophia internascens, Hall 



Page 33 

 Fig. 14. Ventral view of the youngest specimen obser\-ed (length 2 mm.). 



Fig. i4<>. 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. i6fl. Profile of the same; showmg the relative convexity of the valves. 



(Figs. T5-i6a from the 28th Rept N. V. State Mus. Nat. Hist., pi. 26, figs. 49, 45, 44.) 



Rhynchonella indianensis, Hall 



Page 43 



Fig. 17. The earliest stage of growth observed, the shell having a length of .65 mm. The characters are essentially primitive; 



the surface is without plications, the foramen triangular and devoid of plates, or even marginal thickening. 

 Fig. i7rt. Outline profile of the same; showing the elevation of llie ventral umbo. 

 Fig. 18. A later stage of growth In which the shell has a length of 1.5 mm. With the formation of the first growth-line, a number 



of faint plications have appeareit, and the margms of the foramen have become thickened. 

 Fig. i8a. Outline piohle nf 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, Hg. 6, ( 

 Fig. 30. Dorsal view of a larger example, natural si/e, havmg two plications on the fold, and abnormal in the absence of all lateral 



plications ia/. t/V., fig. 5). 

 Fig. 21. Dorsal view of a small, essentially mature example, with two plications on the fold (o/. c/i., fig. 4). 

 Fig. 33. Dorsal view of an adult with three plications on the fold. (38tn Rept. N. V. State Mus. Nat. Hist., pi. 26, fig. 13.) 

 Fig. 33. Front view of an adult with four plications on the fold (c/. ct/, , fig. 23) 

 Fig. 34. Dorsal view of a similar individual. 

 Fig. 34^. Profile of the same {o/- ci/., figs. 15, 19). 



Fig. 35. An enlargement of the cardinal area in an individual with a length of i .5 mm.; showing essentially the primitive charac- 

 ters seen in fig. 17. 

 Fig. ayt. Outline profile of the same. 

 Fig. 36. 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. 

 P"ig. 26rt. Outline profile of the same. 

 Fig, 37. The cardinal features in an individual of 7 mm. length. The advance upon the last stage is chiefly in rapid development 



of the deltidial plates, which have narrowed the opening, slightly constricting it near the now incurved umbo. 

 Fig. aja. Outline piofilc of the same. 

 Fig. 38. The cardinal features in an adult, having a length of lo mm. The deltidial plates have united at their base, forming an 



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

 Fig. 2Ba. Outline profile of the same. 



