PLATE XIX 

 HOIVKEOSPIRA EVAX HALL (PAGES 360-365) 



See Plate XXII 



FIGURE 1. Dorsal view of the youngest individual observed ; having 

 a length of 1 mm. and a width of .8 mm. The ventral umbo is erect, 

 the foramen triangular and without deltidial plates ; the surface bears 

 two faint lines of growth, and outside the second of these are three fine 

 plications on each side of a median sinus. 



FIGURE la. Outline profile of the same ; showing the very shallow 

 valves. 



FIGURE 2. Dorsal view of an average adult ; showing the characters 

 of advanced growth. 



FIGURE 2a. Profile of the same. (28*7* Rept. N. Y. State Mus. Nat. 

 Hist., pi 25, figs. 14, 18.) 



FIGURE 3. Dorsal view of an immature individual 5mm. in length, 

 in which the plications on the earlier portion of the shell end abruptly at 

 a growth-line, from there outward the surface characters being altogether 

 primitive. 



FIGURE 3a. Outline profile of the same. 



FIGURE 4. The cardinal area in its earliest observed condition ; en- 

 larged from figure 1. 



FIGURE 5. A later stage of growth in the cardinal area, the deltidial 

 plates having a considerable development. 



FIGURE 6. A still later condition of this area, in which the plates 

 have united, enclosing the foramen. 



FIGURE 7. The cardinal portions of an individual with an unusu- 

 ally elevated ventral umbo ; showing also an advance in growth from the 

 condition represented in figure 6. 



FIGURE 8. The character of the cardinal area in a normal adult of 

 about the size represented in figure 2. The foramen has become circular, 

 and the ventral umbo so incurved as to conceal the deltidial plates. 



FIGURE 9. A small obese example in which the foramen is almost 

 wholly concealed. 



HOMCEOSPIRA SOBRINA SP. NOV. (PAGES 366-369) 



FIGURE 10. The youngest shell observed ; having a length of 2 mm. 

 and a width of 1.6 mm. The shell already bears two plications on each 

 side of the median sinus, and two much fainter elevated striae in the sinus 

 itself. 



