54 University 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. 
HELICIDAE 
Thysanophora plagioptycha (Shuttleworth) —Fight speci- 
mens from leaves and humus in the lowland forests (H, I, a). 
Thysanophora pilsbryi, new species 
Figs. II, 12, 13, 14 
One specimen from humus in the lowland forest along La 
Laie, Cal, il, 2))c 
Shell minute, depressed, whitish horn-colored; whorls 3%, 
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 whorl (fig. 11). Measurements: altitude, .71 mm.; 
