PTERODISCUS. 125 



dish-brown with some yellowish streaks along the wrinkles, 

 which are quite coarse on the last whorl. The periphery may 

 be either clean or heavily loaded with foreign material. The 

 outline of the base is slightly convex, and it is distinctly 

 angular around the umbilicus, which is one-fourth the total 

 diameter. The columellar lamella is excessively weak and 

 brownish in even fully adult shells. Its position is indicated 

 inside the umbilicus by a slight furrow. A clean adult meas- 

 ures : alt. 3.5, diain. 8.2 mm. ; whorls 4. 



3a. P. wesleyi cwaensin, n. subsp. PL 23, fig. 10. 



The form from Ewa in the C. M. Cooke collection, is prac- 

 tically typical in shape and sculpture, but the columellar 

 lamella is decidedly stronger, being distinct and whitish. 



In the type of wesleyi the columellar lamella is represented 

 only by a very inconspicuous ridge hardly noticeable. 



4. P. THAANUMI n. sp. PI. 24. figs. 1, 2. 



The shell is lens-shaped, umbilicate, the umbilicus contained 

 nearly 5 times in the diameter of the shell, fragile, but 

 slightly shining, dull brown, with sculpture of fine retractive 

 strias and on the last whorl some coarse wrinkles. Whorls 

 4, the second with a margin above the suture, the first two 

 fiat, the rest nearly so; last whorl carinate, convex beneath, 

 not distinctly angular around the umbilicus. Peristome 

 fragile; columellar margin dilated. Columellar lamella thin 

 but rather strong, sloping slightly downwards, becoming very 

 weak on the dilation of the lip. Alt. 4.2, diam. 9.7 mm. 



Oahu: Kukaeiole, near Kaaawa, on the northeastern coast 

 (D. Thaanum) ; type no. 95045 A. N. S. P. 



This species has a. narrower umbilicus than P. wesleyi, but 

 wider than in P. rex or P. cookci. It is less angular around 

 the umbilicus, the base not rising so high there. The colu- 

 mellar lamella is stronger than in P. ivesleyi. 



The embryo (pi. 25, figs. 1, 2, 3) is about 2.6 mm. in dia- 

 meter, with 1% whorls. The first has microscopic crinkling 

 of the cuticle as noticed in P. alatus litus. but the stria? on 

 the second whorl are finer than in that form. There is an 



