130 PLANAMASTRA. 



ancestor which had become differentiated from Amastra by 

 this character; but while Pterodiscus retained the Amastroid 

 columellar lamella, this was early lost in the Planamastra 

 phylum, <and no trace of it remains even in embryonic shells. 



1. P. DIGONOPHORA (Ancey). PI. 24, figs. 9, 10, 11. 



"Shell depressed, sublenticular, scarcely shining, rather 

 thin, opaque, very broadly umbilicate (the umbilicus conic, 

 showing all the whorls, surrounded by a projecting angle, 

 4 mm. wide), irregularly, obliquely and rather roughly sculp- 

 tured with gro wth-lines ; chestnut brown. Spire flat. 

 Whorls 4, rather rapidly increasing, flattened, separated by 

 an impressed and simple suture; the last whorl having pro- 

 jecting angles above and around the umbilicus, flat above, 

 conically tapering below the upper angle, not descending in 

 front or very gradually descending. Aperture somewhat ob- 

 lique, somewhat ax-shaped, biangulate outwardly; peristome 

 acute, the margins joined by a very thin callus. Alt. 214, 

 diam. maj. 6i/ 2 , min. S 1 /^ mm.'' (Ancey). 



Oahu: Waianae (Baldwin). 



Patula digonophora ANCEY, Bull. Soc. Malac. France vi, 

 1889, p. 111. --Pterodiscus digonoph orus Anc., SYKES, 

 Fauna Hawaiiensis p. 292. 



In this species the upper surface resembles that of normal 

 forms of Pterodiscus, the embryonic sculpture being similar, 

 the second whorl more or less distinctly marginate above the 

 suture, and the periphery carinate. The lower surface differs 

 by the very broadly open umbilicus and the absence of any 

 trace of a columellar lamella, at all stages of growth. The 

 specimens figured were received from Mr. Baldwin. An adult 

 measures, alt. 2.7, diam. 7 mm., whorls 3%. The embryonic 

 shell figured (pi. 25, figs. 4-6) has a diameter of 1.8 mm. with 

 whorls. 



2. P. PEASEANA n. sp. PI. 25, figs. 8, 9, 10. 



The shell is discoidal, with very low, convex spire, openly 

 umbilicate base, and acutely carinate periphery ; thin ; corne- 

 ous, with a brown band revolving in the middle of the upper 



