CAMAROTCECIIIA ACINUS Hall (Pages 339-341) 



Figure 9. — Ventral view of a young shell in a secondary stage of 

 growth ; showing a single growth-line and the embryonal median ridge. 



Figure 9rt. — Doi'sal view of the same. The foramen is slightly nar- 

 rowed, but without evidence of deltidial plates; the embryonal sinus is 

 well defined. 



FiGUitE Oh. — Outline profile of the same. 



FiGUP.E 10. — Ventral view of a specimen 3.25 mm. iu length. 



Figure 10a. — Dorsal view of the same. The mature fold and sinus 

 have not yet begun to develop ; the foramen shows increased constriction 

 at its base, and slightly tliickened margins. 



Figure 10?'. — Outline profile of the same. 



Figure 11. — Dorsal view of an average adult. X i- 



Figure 11a. — Profile of the same. 



Figure 116. — Front view of the same; showing tlie elevation of the 

 median fold. 



PJIYNCIIOTPtETA CUNEATA Dalman, var. AMERICANA 

 Hall (Pages 351-356) 



See Plate XXII 



Figure 12. — Dorsal view of a shell representing the earliest stage of 

 growth observed; length 1.5 mm. The foramen is widely triangular and 

 unobstructed, the surface is covered with all the plications of maturity, 

 and the sub-circular valve bears a broad median depression. 



Figure 12a. — Outline profile of the same. 



Figure 13. — Similar view of a shell 3 mm. in length. The outline 

 has become elongate, the foramen narrowed, and its margins thickened. 



Figure 13a. — Outline profile of the same. 



Figure 14. — Dorsal view of a normal adult individual; showing the 

 elevated beak and broad plications. Natural size. 



Figure 14o. — Profile of the same; showing the elevation of the dor- 

 sal fold. 



Figure 14&. — Front view of the same. (28th Rcpt. X. Y. Stale I\fits. 

 Nat. Hist., pi. 25, figs. 31, 34, 36.) 



Figure 15. — A series of outlines of the anterior margin ; showing 

 the embryonal sinus or depression in the dorsal valve in young forms, 

 reaching its maximum in individuals having a length of 4.5, and becom- 

 ing obsolete, or the line of junction straight, in specimens 7 mm. in 

 length. Outline shows the inception of the dorsal fold. In 8 the four 

 median plications are distinctly elevated ; 9 is from a normal full-grown 

 individual, and 10 represents the maximum elevation of the fold. The 

 outlines, except in 9 and 10, are enlarged to the diameter of a fully 

 developed specimen. 



Figure 16. — Cardinal area of figure 12. 



Figure 16o. — Outline profile of the same. 



