PLATE XVI 

 LEPT.ENA RHOMBOIDALIS AVilckens (Pages 322-327) 



Figure 1. — Ventral view of the youngest shell observed, its length 

 being 1.25 mm. The aperture of the embryonal pedicle-sheath is very 

 conspicuous, and its margins are very thick. The surface shows a faint 

 median depression, indications of two concentric growth-lines, and out- 

 side the latter of these, obscure traces of plications. 



Figure la. — Outline profile of the same; showing the prominence of 

 the sheath. 



Figure 2. —Ventral view of an individual with a lengtli of 2 nun. 

 The aperture of the pedicle-sheath is relatively somewhat diminished in 

 size, its margins have become thinner, and the radiating plications nu- 

 merous and sharply defined. 



Figure 2a. — Outline profile of the same; indicating diminution in 

 the prominence of the sheath. 



Figure 3. — Ventral view of an individual having a length of i mm. ; 

 showing the inci-ease in the number of plications, the appearance of nu- 

 merous concentric undulations and strife, and the narrowing pedicle- 

 aperture. 



Figure da. — Outline profile of the same ; showing the concentric 

 undulations and the diminishing pedicle-sheath. 



Figure 4. — Ventral view of a normal adult, having a length of 

 28 mm.; showing the cliaracters of maturity. Natural size. 



Figure 4rt. — Profile of another individual of full growth; showing 

 the anterior geniculation and the length of the anterior slope, or curtain. 

 (28th Kept. N. Y. State J\fus. Nat. Hist., pi. 22, figs. 6, 7.) 



Figure 5. — Cardinal view of the specimen represented by figure 1. 



Figure 6. — Similar view of the specimen represented by figure 2. 



Figure 7. — Similar view of an individual 2.65 mm. in length. 



Figure S. — Similar view of the specimen represented by figure 3. 



Figure 9. — Similar view of an individual 9 mm. in length. 

 These cardinal views are drawn with the same degree of enlargement, 

 and show the gradual diminution in height and in diameter of aperture 

 in the pedicle-sheath, and the increasing development of the grooved 

 callosity on the dorsal valve. 



Figure 10. — Cardinal view of a normal adult; showing tJie great 

 size of the grooved callosity, and the crecal opening, representing the 

 atrophied pedicle-sheath. Natural size- (op. cit., fig. 10.) 



