388 THE TERRESTRIAL MOLLUSCA INHABITING 



P. YouNQi, Garrett. 



Pitys Youngi, Garr., Amer. Jonr. Conch., 1872, p. 229, PI. 19, fig. 22. 



Patula Toungi, Schraeltz, Cat. Miis. Godeff., v. p. 93. 



Helix Youngi, Pfeiffer, Mon. Hel., vii. p. 543. 



This species, which is also peculiar to Harotonga, is somewhat rare, and only 

 occurred to my notice in one valley, the habitat of the typical decorticata. 



It differs from canalis in the total absence of spots and stripes, lighter color, 

 more elevated spire, broader and flatter whorls, and smaller umbilicus. The 

 description (1. c.) should read 4, not 4|, whorls, which is one less than in canalis. 



P. PLANOSPIRA, Garrett. 



Shell small, broadly umbilicated, discoidal, thin, with slightly oblique, rib-like, 

 crowded striee; horn color rayed and tessellated with brown; spire planulate ; 

 suture deeply impressed; whorls six, convex, slowly and regularly increasing, last 

 one rounded, not deflected in front, flatly convex beneath ; umbilicus large, per- 

 spective, one-third the major diameter of the shell; aperture oblique, rather 

 narrowly lunate ; peristome thin, simple. 



Major diameter 3, height 1| mill. (Mus. Godeffroy). 



Hab. Earotonga Island. 



A very rare species characterized by its peculiar flat spire, depressed base, 

 numerous narrow whorls, and broad umbilicus. As viewed from above it closely 

 resembles the next species in its narrow whorls, but is smaller, the ribs finer, and 

 the planulate spire will at once separate them. 



P. TJNILAMELLATA, Garrett. 



Fitys unilamellata, Garr., Proc. Phil. Acad. Nat. Sci., 18t3, p. 235, PI. 3, fig. 6t. 



This is also a very rare species, peculiar to Earotonga. The single revolving 



lamina on the parietal region will readily determine it from any of the preceding 



species, and is one of those species which by the development of a parietal lamina 



connects Patula with the following genus. 



GENUS PITYS, Beck. 



I restrict this genus to a group of small Helices, the type of which is Helia; 

 Oparica, Anton. So far as known, they are peculiar to the South Sea islands, and 

 have their metropolis in Southeastern Polynesia, where they are the most numer- 

 ous, both in species and individuals. They have spread north to the Sandwich 

 Islands, and west to the Viti Group. 



They may be distinguished by their depressed orbicular form, narrow whorls, 



