Occasional Papers of the Museum of Zoology 



47 



tado") to practically the same conditions as the original forest 

 (H, V, b, 41). Such isolated occurrence in second-growth 

 seems to favor the hypothesis that this is an introduced species. 

 The columellar denticle in these shells is quite low and 

 rounded, but in no sense vestigial. The first iVj whorls are 

 lightly and irregularly pitted. In addition to the prominent, 

 growth ribs, the surface of their interspaces is covered with 

 microscopic sculpture. The latter consists of rounded spiral 

 riblets, which are broken, by impressed growth lines, into 

 series of Ijead-like prominences. 



Figure 21. Adclopoma occidcntalc. Teeth of half-row, separated 

 laterad. Al tlie right is shown a ventral view of another of the outer- 

 most teeth. The scale indicates a length of 50 microns. 



Figure 21 shows a half row from the radula of this species, 

 with the teeth separated laterad, so as to better show their 

 form. As usually seen, the first lateral overlaps the central, 

 while the bases of all of the laterals and marginals are crowd- 

 ed closely together. The right-hand figure of the marginal 

 tooth shows the ventral side uppermost. The denticle, near 

 the center of the base of the rachidian tooth, is very promi- 

 nent and distinctlv reminiscent of the Amnicolidae. As will 



