122 PTERODISCUS. 



were from Newcomb, it may be inferred that they were from 

 the same lot. In view of Dr. Pfeiffer's well-known accuracy 

 as a diagnostician, it is hard to believe that his description 

 of Helix alata was based upon the same species, since it dis- 

 agrees in the number of whorls and shape of the spire, and 

 in omitting a reference to the columellar lamella. 



The shell, in Newcomb 's specimen (pi. 22, figs. 1-3), is 

 thin, umbilicate, biconvex, the base more convex than the spire, 

 periphery carinate. Brown, nearly lusterless. Whorls 4, 

 the first nearly smooth, hardly convex, the second flat, 

 obliquely striate, with a peripheral marginal cord, the next 

 whorl densely marked with growth-stria?, convex near the 

 periphery but without a margining cord. Last whorl barely 

 convex, sloping above, densely marked with growth-stride and 

 on its later portion with some coarse oblique wrinkles; con- 

 vex beneath. Umbilicus rather narrow and tubular, its width 

 contained about 6 limes in the diameter of the shell. Aper- 

 ture wider than high, the dilated columellar lip bearing an 

 acute, subhorizontal lamella. Alt. 4.3, diam. 8.2 mm. 



The peristome is broken in the specimen figured, which 

 has no wing of foreign material adhering to the periphery. 



la. P. ALATUS LITUS n. subsp. PI. 22, figs. 4, 5, 6. 



The shell is lens-shaped, the base usually more convex than 

 the top, keeled, thin and fragile, dull, brown. The whorls 

 are flat above ; the first half of the second whorl is margined 

 above, as usual. Sculpture of very fine, close, retractive 

 striae, and on the last whorl some coarse wrinkles in the same 

 direction. The base is somewhat convex, not strongly angular 

 around the umbilicus. It is more or less copiously smeared 

 with dirt, which at the periphery forms an irregular flange. 

 The umbilicus is very narrow, tubular, about one-eighth the 

 diameter of the shell. Columellar margin dilated, thickened 

 within in adults, and bearing a strong, subhorizontal lamella. 



Alt. 4.7, diam. 10 mm.; whorls 3%. (no peripheral flange). 



Alt. 4.3, diam. including flange 11.5 mm. 



Alt. 5, diam. 9.5 mm. (no peripheral flange). 



Lanai (D. Thaanum). Types 94501 A. N. S. P. 



