I'LATI-: XVI 



LEPT.KNA UIIOMIiOIDALIS Wilckkxs (Pages •'i22-:527) 



FiGUni'. 1. — Ventral view of the youngest shell obscrvc'il, its length 

 being l.l'O mm. The ain'ihii-K of the eiiilivyonal pedicle-sheath is very 

 conspicuous, and its margins are very thick. 'J'he surface shows a faint 

 median deprc^sion, indications of two cnnc(.'ntric growth-lines, and out- 

 side the latter of these, obscui'e traces of plications. 



Fi(iui;io la. — Outline profile of the siim(!; showing the prominence of 

 the sheath. 



Figure 2. —Ventral view of an individual with a length of 2 mm. 

 The aperture of the pcdiele-sjieath is relatively somewhat dindnished in 

 size, its margins have becf)me thinnei', and the radiating plications mi- 

 merous and sharply defined. 



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

 the prominence of the sheath. 



FiGUi'.io •!. — Venti"al view of an individual having a lenj^tli of I mm. ; 

 showing the increase in the number of plications, the appearance of nu- 

 merous concentric undulations and strire, and the narrowing pedicle- 

 aperture. 



FiGURi; 3«. — Outline profile of the same; showing the concentric 

 undulations and the diminishing pedicle-sheath. 



FicuRK 4. — ^'l'ntral view of a normal adult, having a length of 

 2SHini.; showing I he r|iara(.'ters of maturity. Natural size. 



Figure \a. — I'roflle of another individual of full gni«tli; showing 

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

 (2Slh Repl. N. Y. Stale Mux. Nat. Hist., pi. 22, figs. 6, 7.) 



FiGUiiE •"). — Cardinal \ iew of the specimen represented by figujc 1. 



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



Figure 7. — Similar view of an individual 2.6.5 mm. in length. 



Figure ^s. — Similar view of the specimen represented by figure :j. 



FiGi'RE 9. — Similar view of an individual 9 mm. in length. 



The>.e 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 the great 

 size of the grooved callosity, and the ca'cal opening, repre.senting the 

 atrophied pediele-sheadi. Natural size. (op. a7., fig. 10.) 



