PLATE XVII 

 STROPHONELLA STRIATA HALL (PAGES 330-334) 



FIGURE 1. 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. 



FIGURE la. Outline profile of the same ; showing the complete con- 

 vexity of the ventral valve, and essentially conformable concavity of the 

 dorsal valve. 



FIGURE 2. Ventral valve of a normal adult ; showing the umbonal 

 convexity of the shell and general concavity over the pallial region. 

 (28*7* Rept. N. Y. State Mus. Nat. Hist., pi. 23, fig. 1.) 



FIGURE 2a. Outline profile of the same ; showing the reversal in 

 convexity from the embryonic condition. 



FIGURE 3. Pedicle-area of the specimen represented in figure 1 ; 

 length 2.25 mm. ; showing the well-developed, slightly exsert sheath 

 and the obscure dorsal callosity. 



FIGURE 4. Pedicle-area of an individual 2.5 mm. in length, in 

 which the sheath is extravagantly exsert. 



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



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



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



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

 length. 



Figures 3-8 have been drawn to the same scale, and show the succes- 

 sive 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 eventu- 

 ally separated from the sheath by a narrow aperture, and its surface 

 becomes uninterrupted. 



MIMULUS WALDRONENSIS MILLER AND DYER (PAGES 334, 335) 



FIGURE 9. Dorsal view of a young individual having a length of 

 3 mm. The shell is nearly symmetrical, and shows an open triangular 

 deltidium, ending in a sub-circular apical foramen. 



FIGURE 9a. Ventral view of the same ; showing the apical foramen. 



FIGURE 96. Outline profile of the same. 



