PLATE XXI 



MElirSTIXA MARIA Hall (Vac.ks :377-:)8()) 



FiGUKE 1. — An embryo ineasuriiig .7') X .7-) iniu. ; ^YilllOut di'ltidial 

 plates. 



FiGur.E la. — Outline jtrotile of the s;iine. 



Fig u UK 2. — A Inter staoo of growtli, at which the shell measures 

 T) X 5 mm., and the deltidial plates have develojied sufficiently to give 

 the foramen a circular outline. 



FiGUKK 2ii. — Outline profile of the same. 



FiGUHK 3. — Dorsal view of a normal, mature shell. 



Figure 3r/. — I'lofile of the same. (28th A7vi. Kept. N. Y. Slate Mits. 

 Nat. Hist., pi. -Jo, figs. 9, 12.) 



MERISTINA RECTIROSTRIS Hall (Pages ;572-374) 



FiGUHE 4. — Tlic cardinal featui'es at an extremely early stage of 

 growth, the shell measuring 3 X - mm. ; showing the broad, triangular 

 foraminal oiKMiing and its faintly thickened margins. 



FiGUKE 4a. — Outline profile of the same. 



FiGUKE 5. — The same features when the shell has attained a size of 

 4.-5 X 3..') mm. ; .-.liowing the gradual ajuiroximation of the sides of fora- 

 men and the narrowing of the umbo, without the formation of deltidial 

 plates. 



Figure 5a. — Outline profile of the same. 



Figure 13. — The same features at nniturity. 



Figure 13c;. — Outline jirofile of the same. 



FiGUitE 11. — Dorsal view of a young individual. 



Figures 12, 12^, V2h. — Dorsal, profile, and ventral views of an adult 

 specimen. (ll//t Ann. L'ept. Geol. Sure. Iiu/., ]il. 27, figs. 1, 10-12.) 



WIIITFIELDELLA XITIDA Ham. (Pages 371-377) 



Figure 10. — Dorsal view of the youngest individual observed; hav- 

 ing a size of 2.5 X 1.75 nun. 



Figure 10a. — Outline profile of the same. 



Figure (i. — Cardinal features of a sliell liaving dimensions of 3 X 2 

 mm. 



Figure Ga. — Outline pnifile of the same. 



Figure 7. — 'I'he same features in an individual having a size of 

 f) X 4 mm. In this example the umbo is abnormally elongate, giving an 

 unusual )>rominence to the delti<lial ]tlates. 



FuiURE 7a. — Outline profile of the same. 



Figure 8. — The same features at a size of 5 X 4 mm. ; showing the 

 total ctnicealment, from incurvature, of the deltidial ])lates. 

 Figure 8a. — Outline ])rofile of the same. 



Figures !), '.)a. i)h. — Dorsal, ventral, and jirolile \ iews of the noiiual 

 adult. (2S//, Ami. lU'pt. N. Y. Si„lr ^f,ls. .\al. Ifisl.. ].l 25, figs. 3, 1, 5.) 



