OF CONCHOLOGY. 227 



remote lamella, and two on the parietal region ; peristome thin, 

 sharp, slightly sinuous, continuous with the acute umbilical mar- 

 gin ; columella with a single fold, sinuous. 



Diam., 6 mill.; height, 4 mill. 



Habitat, Rarotonga Isl., Cook's Isles. (Coll. Garrett and Phila, 

 Acad.) 



This is also a Marsupial species, which we gathered in abun- 

 dance in the mountain ravines, It is more closely allied to H. 

 fratercula, Pse., than the preceding species. The latter species 

 never occurs inland, and is more stoutly ribbed, lighter colored, 

 the carina stouter and beautifully corded. 



Pitys canalis, Garrett. Plate 19, fig. 17. 



Shell widely umbilicate, flatly discoid, thin, subpellucid, 

 slightly glossy, closely and very finely ribbed, ribs oblique, sin- 

 uous, light brownish horn color, with darker radiating spots ; 

 spire very flat, not rising above the penultimate whorl ; suture 

 deeply channeled ; whorls 5, strongly convex, regularly increas- 

 ing, last one declivous above the periphery, rounded below ; um- 

 bilicus deep, perspective, freely exposing all the whorls, nearly 

 half the diameter of the shell ; aperture oblique, sinuously 

 rounded ; peristome thin, simple, slightly sinuous. 



Diam., 6 mill. ; height, 2 mill. 



Habitat, Rarotonga Id., Cook's Isles. 



A somewhat rare species, found on the ground in damp for- 

 ests, and confined to a single valley. Its flat spire, deeply chan- 

 neled suture, and very wide umbilicus are its most important 

 characters. 



Pitys rudis, Garrett. Plate 19, fig. 18. 



Shell umbilicate, subdiscoid, thin, subpellucid, very finely la- 

 minately ribbed, ribs rude, sinuous, more or less irregularly dis- 

 posed, or even altogether wanting, interstices under the lens 

 very finely striated, horn color, brownish, sometimes brownish- 

 black, with or without reddish-brown rays ; three upper whorls 

 of the spire flat ; suture channeled ; whorls 4£, strongly convex, 

 rather rapidly increasing, last one rounded below, slanting above 

 the periphery; umbilicus deep, about one-fourth the diameter of 

 the shell ; aperture sinuously circular ; peristome thin, simple 



Diam., 3^ mill. ; height, 2 mill. 



Habitat, Rarotonga Id., Cook's Isles. (Coll. Garrett and Phila. 

 Acad.) 



