PLATE XVII 

 STROPIIONELLA STRIATA IIai.i. (Paoks 330-334) 



Fi(;UKK. 1. — Veiitnil view ol' llir iiici[)itMit sln'll nf llu' si'i'ics ; Icii^tli 

 2.25 iinu. ; showing tlie opening' of llic pediele-.sheuth, and Mic priimtry 

 siirluce plications. 



FiGUKE \(i. — Ontline profile of the same; showing tlie complete con- 

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

 dorsal valve. 



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

 convexity of the shell and genei-al concavity over the pallial region. 

 {•2Sth ne/jt. V. }'. Stale Mus. Nat. Hist., pi. 23, fig. 1.) 



Fjguuk 2a. — -Outline profile of the same; showing iiie reversal in 

 convexity from the end)ryonic 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 1. — I'edicle-area of an individual 2.5 mm. in length, in 

 which the sheath is extravagantly exsert. 



Figure 5. — Fediclearea in an example about 6 mm. in length. 



FiGiTRE G. — Pedicle-area, when a length of 8 mm. has been attained. 



Figure 7. — Pedicle-area in a shell measui-ing 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. 'I'he sheath 

 ceases its function as a pedicle-passage before maturity is attained, 

 though retaining its relative size; while the dorsal callosity, which in tln^ 

 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. 



IMIMII.r.S WALDltOXEXSIS Mii.i.ki: am. DyFi: (Packs 3:51. :535) 



Figure 9. — Dorsal view of a young individual having a length of 

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

 deltidiuin, ending in a sub-circular apical foramen. 



Figure 9a. — Ventral view of tlie same ; showing the apical foiamen. 



Figure Oh. — Outline profde of the same. 



