.PKUKESTKIAL MOI.LCSOA INHABITING SOCIKTY ISLANDS. 
r.*C.I.oo.rA,Mo,...o»,MS. Pl.IC II, ligs. 13. 6 
— - 
“ «?;Tde.y nmWHcatod. depie^ed-orbiculav. coineous ivMi reddish 
lions; radio, ely striated with thin, rather closely 
flatly convex, apex plaiiulate; suture deeply impressed ; whorls fi^e, con > 
and regularly increasing, turgid next to the suture, last one slightly ( ^ 
not descending in front, base convex; umbilicus large, perspective, exhibiting all the 
uhorls, about one-third the major diameter of the shell; aperture nearly vertical, 
irregularly orbicular-lunate; parietal region with one or two, very rarely three laminae; 
peristome simple, straight, Avith remote margins. 
Major diara. 4;|, height 2 mill. 
A very rare variety occurs which is uniform whitish horn-color. 
As compared with* consimiZis it is larger, more depressed, umbilicus larger and ribs 
P. L.AMELLicosTA, GaiTett. Plate II, figs. 11, 11 a, 11 fc. 
Sliell small, widely unibilicated, orbicular, depressed, thin, subiiellucid, brown or 
liilvous-brown, nnicolored or tessellated with deeper brotvn ; radiately striated witli 
rather distant, oblique, slightly tvaved lamelliforni riblets ; spire flat, not rising above 
tlie ix'nnltimate whorl; suture deeply impressed; Avhorls four, convex, slowly and 
regularly increasing, the last not descending in front, rounded on the ix'riphery, 
obliquely depressed above ; umbilicus more than a third the greater diameter of the 
shell ; aperture oblique, orbicular-lunate. 
Major diam. 3, height I 3 mill. 
Appears to be a scarce species, living beneath rotten wood in damp stsitions at 
Tahiti. It is more openly umbilicated than any other Society Island species. The 
proportion of the umbilicus to the major diameter of the shell is the same as P. 
gradaia, Gld., and the sculpture is similar to P. tenuicostata, Garr. 
Genus PITYS, Beck. 
As Stated in my paper on the “ Terrestrial Mollusca inhabiting the Cook’s or 
Harvey Islands,” published in the Journal of the Academy of Natural Sciences of 
I’hiladclphia, I restrict this genus to those species characterized by the existence of 
laminae on both the parietal region and palate. 
