PLATE VII 



WHITFIELDIA MARIA, Hall 



Page 73 



Fig. 1. An embryo measuring .75X.75 mm.; without deltidial plates. 



Fig. In. Outline profile of the same. 



Fig. 8. A later stage of growth, at which the shell measures 5X5 mm., and the deltidial plates have de- 

 veloped sufficiently to give the foramen a circular outline. 



Fig. 2a. Outline profile of the same. 



Fig. 3. Dorsal view of a normal, mature shell. 



Fig. 3a. Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pi. 25, figs. 9, 12.) 



Meristella rectirostra, Hall 



Page 67 



Fig. 4. The cardinal features at an extremely early stage of growth, the shell measuring 3X2 mm.; show- 

 ing the broad, triangular foraminal opening and its faintly thickened margins. 



Fig. 4(1. Outline profile of the same. 



Fig. 5. The same features when the shell has attained a size of 4.5X3.5 mm.; showing the gradual 

 approximation of the sides of foramen and the narrowing of the umbo, without the formation 

 of deltidial plates. >. < ^1 



Fig. 5<j. Outline profile of the same. / i->— I ^ 



Fig. 13. The same features at maturity. 



Fig. 130. Outline profile of the same. 



Fig. II. Dorsal view of a young individual. 



Figs. 12, I2<i, 12*. Dorsal, profile, and ventral views of an adult specimen, (nth Ann. Rept. Geol. Surv. 

 Ind., pi. 27, figs. 13, 10-12.) 



Meristina nitida, Hall 



Page 70 



Fig. 10. Dorsal view of the youngest individual observed, having a size of 2.5X1.75 mm. 



Fig. lOrj. Outline profile of the same. 



Fig. 6. Cardinal features of a shell having dimensions of 3X2 mm. 



Fig. 6a. Outline profile of the same. 



Fig. 7. The same features in an individual having a size of 6X4 mm. In this example the umbo is 



abnormally elongate, giving an unusual prominence to the deltidial plates. 

 Fig. ya. Outline profile of the same. 

 Fig. 8. The same features at a size of 5X4 mm.; showing the total concealment, from incurvature, of the 



deltidial plates. 

 Fig. Sa, Outline profile of the same. 

 Figs. 9, 9a, gi. Dorsal, ventral and profile views of the normal adult. (28lh Ann. Rept. N. Y. State Mus. 



Nat. Hist., pi. 25, figs. 3, 4, 5.) 



