54 Unh'crsiiy of Michigan 



or less equably throughout the radula, and probably accounts, 

 in part, for the lack of transitional teeth between the laterals 

 and marginals in both species of Guppya s. s. 



Zonitoides (Pseudohyalina) minuscula (Binney). — Eight 

 specimens from humus, and on the underside of leaves and 

 bits of bark on the ground, in the lowland (H, I, a) and the 

 savannah (H, III. a) forests. 



HEUCIDAE 



Thysanophora plagioptycha (Shuttleworth). — Eight speci- 

 mens from leaves and humus in the lowland forests (H, T, a). 



Thysanophora pilsbryi, new species 



Figs. II, 12, 13, 14 



One specimen from humus in the lowland forest along La 

 Laja (H, I. a). 



Shell minute, depressed, whitish horn-colored; whorls 334» 

 gradually increasing in size ; last whorl descending slightly, so 

 that the upper edge of the aperture is at about one-half the 

 height of the preceding whorl ; margin of aperture simple, thin,' 

 and almost circular in outline as far as complete; suture well 

 marked, impressed ; greatest diameter of whorls considerably 

 above middle ; umbilicus large, almost one-third the diameter 

 of the shell, and showing all of the whorls; sculpture of shell 

 consisting of equally spaced, quite regular, delicate riblets, 

 which run parallel with the growth-lines, extend to within one- 

 quarter of a whorl from the apex, and are highest on the upper 

 side of the shell ; entire surface of the shell, as far as could 

 be made out, also covered with delicate striatulations, which 

 cross each other at right angles, but cross the growth-lines at 

 oblique angles, and form minute but extremely regular squares 

 4 microns (.004 mm.) across. This minute sculpture is regu- 

 lar and uniform in spacing from near the apex to the edge of 

 the last whorj (fig. 11). Measurements: altitude, .71 mm.; 



