PLATE XVIII 

 CAMAROTCECHIA WHITII HALL (PAGES 344-346) 



FIGURE 1. The earliest observed stage of growth, the shell measur- 

 ing 2.75 mrn. in length by 2 mm. in width. The deltidial plates have 

 already begun to form along the edges of the triangular foramen, and 

 four pairs of plications are visible on the dorsal valve. 



FIGURE la. Outline profile of the same. 



FIGURE 2. Dorsal view of a normal adult having two plications on 

 the fold. Natural size. 



FIGURE 2a. Profile of the same. 



FIGURE 2b. Front view of the same. (28th Rept. N. Y. State Mus. 

 Nat. Hist., pi. 26, figs. 23, 26, 25.) 



FIGURE 4. The cardinal features of a young example with a length 

 of 3.25 mm. ; showing the inception of the deltidial plates. 



FIGURE 4a. Profile of the same. 



FIGURE 5. Cardinal features of an individual which has attained a 

 length of 6 mm. The umbo has become incurved and the development 

 of the plates is well advanced, but it is arrested at this stage, the foramen 

 not becoming enclosed at maturity. 



FIGURE 5a. Outline profile of the same. 



CAMAROTCECHIA NEGLECTA HALL (PAGE 341-344) 



FIGURE 6. Dorsal view of the youngest shell observed ; having a 

 length of .75 mm., and a width of .5 mm. Though the foramen is open 

 and without evidence of thickened margins, four fine plications have 

 already appeared on the dorsal valve. 



FIGURE 6a. Outline profile of the same. 



FIGURE 7. Dorsal view of an individual with a length of 2.25 mm. 

 The deltidial plates are in an incipient condition and the plications of 

 the surface have considerably increased. 



FIGURE 7a. Outline profile of the same. 



FIGURE 8. Dorsal view of a mature example. Natural size. 



FIGURE 8a. The same in profile. (28th Rept. N. Y. State Mus. Nat. 

 Hist., pi. 26, figs. 3, 5.) 



FIGURE 3. A somewhat abnormal adult, having three plications on 

 the fold and the lateral plications obsolescent. X 2. (llth Ann. Rept. 

 Geol. Surv. Ind., pi. 27, fig. 3.) 



