NATURAL SCIENCES OF PHILADELPHIA. 235 



roundly luniforni, wider than high, fiiuces with three, and the 

 parietal region with two lamellre; peristome thin, simple. 



Diam. 4, height 1^ mill. 



Hah. Rarotonga I., Cook's Isles. (Coll. Phil. Acad. Nat. 

 Sciences.) 



A beautiful species, well characterized by its conspicuous spots 

 and stripes on a pale ground, membranous ribs and fine lamelte. 

 It belongs to the same group as P. modicella, contorta^ and multi- 

 lamellata. 



PiTYS UNiLAMELLATA, Garr., pi. 3, fig. G7. 



Shell umbilicate, sub-discoid, thin, corneous, tessellated, and 

 rayed with brown, plicately ribbed, ribs compressed, rather closely 

 set, regular, oblique, flexuous, finer and more crowded beneath ; 

 spire depressl^'' convex, apex prominent ; whorls 5, convex, slowly 

 and regularl}'- increasing, last one not descending in front, obtusely 

 sub-angular on the periphery, and more distinctly so on the um- 

 bilical region ; suture channelled ; umbilicus large, freely exposing 

 the whorls, nearly one-third the greatest diameter of the shell; 

 aperture oblique, somewhat rhomboid luniform, wider than deep ; 

 parietal region with a single small lamella ; peristome thin, simple. 



Diam., greatest 4^, height 2 mill. 



Hah. Rarotonga I., Cook's Isles. (Coll. Phil. Acad. N"at. 

 Sciences.) 



A rare species found under decayed vegetation in mountain 

 ravines. 



Plecotkema ttjreita, Garr. pi, 3, fig. 68. 



Shell sub-perforate, solid, more or less acutely ovate, turreted, 

 transversely finely ridged, ridges closely set, granulated, interstices 

 crossed by raised lines, corneous with white lips ; spire sub-acute, 

 turreted, conical ; whorls *7-8, flat, tabulate above, last one large, 

 ovate-globose, sulcate next the suture, angular at the base ; aper- 

 ture oblique, narrow, oblong, contracted ; peristome with a large 

 sub-marginal external varix, rather thin, slightly expanded, an- 

 gular above, then obliquely descending towards the base, where it 

 is rounded and continuous with the labiate callosity on the colu- 

 mella and parietal region ; inner margin labiate, with a median 

 tubercle ; columella with a transverse fold, a second one on the 

 parietal region, and a tubercle above. 



Length 4i mill. 



