30 TERRESTRIAL MOLLUSCA INHABITING SOCIETY ISLANDS. 
P. acuricosta, Mousson, MS. Plate IT, figs. 138, 13 a, 13d. 
Patula acuticosta, “‘ Mousson,” Schmeltz, Cat. Mus. Godeff., v, p. 93. 
Helix acuticosta, Pfeitter, Mon. Hel., vii, p. 480. (Name only.) 
Though less abundant, is, like consimilis, confined to Raiatea. 
So far as I can ascertain, there has been no description published, I subjoin the 
following :— 
Shell widely umbilicated, depressed-orbicular, corneous with reddish brown tessella- 
tions; radiately striated with thin, rather closely set, slightly arcuate, riblets; spire 
flatly convex, apex planulate ; suture deeply impressed; whorls five, convex, slowly 
and regularly increasing, turgid next to the suture, last one slightly depressed above, 
not descending in front, base convex ; umbilicus large, perspective, exhibiting all the 
whorls, about one-third the major diameter of the shell; aperture nearly vertical, 
irregularly orbicular-lunate ; parietal region with one or two, very rarely three lamine; 
peristome simple, straight, with remote margins. 
Major diam. 44, height 2 mill. 
A very rare variety occurs which is uniform whitish horn-color. 
As compared with consimilis it is larger, more depressed, umbilicus larger and ribs 
finer. 
P. LAMELLICosTA, Garrett. Plate II, figs. 11, lla, 116. 
Shell small, widely umbilicated, orbicular, depressed, thin, subpellucid, brown or 
fulvous-brown, unicolored or tessellated with deeper brown; radiately striated with 
rather distant, oblique, slightly waved lamelliform riblets; spire flat, not rising above 
the penultimate whorl; suture deeply impressed; whorls four, convex, slowly and 
regularly increasing, the last not descending in front, rounded on the periphery, 
obliquely depressed above; umbilicus more than a third the greater diameter of the 
shell; aperture oblique, orbicular-lunate. 
Major diam. 3, height 15 mill. 
Appears to be a scarce species, living beneath rotten wood in damp stations 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. 
gradata, Gld., and the sculpture is similar to P. tenuicostata, Garr. 
4 
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 
Philadelphia, I restrict this genus to those species characterized by the existence of 
lamin on both the parietal region and palate. 
