PTERODISCUS. 121 



in diam. of shell; col. lam. rather strong; 4.2x 

 9.7 mm., 4 whorls. Near Kaaawa. 



P. thaanumi, no. 4. 



c 4 . Upper surface convex ; umbilicus GI/O to 9 times 

 in the diam. of shell ; lamella weak ; 6x11 to 

 4.5x10.5 mm., 4 1 / whorls. Nuuanu. 



P. cookei, no. 6. 



c r '. Spire very low; umbilicus moderate; lamella 

 rather strong; 14.5x4 mm., 5 whorls. Kona- 

 huanui. P. rex, no. 5. 



I) 1 . Spire widely conic; whorls 5, the last carinate ; um- 

 bilicus contained 5 times in the diameter ; Waianae. 



P. heliciformis, no. 7. 



1. P. ALATUS (Pfeiffer). PI. 22, figs. 1-3. 



" Shell narrowly umbilicate, depressed, membranaceous, 

 obliquely irregularly striate, having an oily luster, pellucid, 

 brownish-corneous. Spire nearly flat. Whorls 3i/o, rapidly 

 increasing, the last angular, encircled with a thin, deciduous 

 wing-like carina, dilated in front. Base convex. Aperture 

 very oblique, securiform. Peristome simple, unexpanded, the 

 basal margin very deeply arcuate. Alt. 3, greater diam. 

 81/0, lesser 6 mm." (Pfr.) 



Lanai (Newcomb). Mountains behind Koele (Perkins). 



Helix alata PFR., P. Z. S. 1856, p. 33; Monographia Hel. 

 Viv. iv, p. 116. Amastra (Kauaia) alata Pfr., SYKES, Fauna 

 Hawaiiensis, Mollusca, p. 355. Amastra (Helicamastra) 

 alata Pfr., PILSBRY and VANATTA, Proc. A. N. S. Phila. 1905, 

 p. 571, pi. 38, f. 4-6. 



Mr. E. R. Sykes who examined the type of this species 

 writes: "this shell has a columellar plait. It is, in my 

 opinion, not a Helicoid at all, but, belongs to an aberrant 

 group of Amastra. The columellar plait does not ascend 

 rapidly into the shell, but stands almost horizontally, and 

 has no final knob." 



The specimen described below and figured on plate 22, 

 is from Newcomb 's collection, and since Pfeiffer's types 



