AMASTRA, KAUAI. 147 



rontic specimen (pi. 16, fig. 6) in coll. C. M. Cooke is very 

 solid, the outer wall thick, parietal wall covered with a thick 

 white callus which bears a low, wide, conical prominence, a 

 short distance within. The columella is heavily white-cal- 

 loused, and its spiral lamella is thick, blunt, and hardly dif- 

 ferentiated from the basal truncation of the pillar. The 

 specimen is dead and almost wholly denuded of the thin yel- 

 low cuticle. 



' ' The species is very rare. We dedicate it to Mr. A. Knud- 

 sen, the young naturalist who discovered it. He writes that 

 it is of very limited distribution, being found far up the 

 mountain only in an isolated tract of woodland which escaped 

 the forest fires of twenty years ago. In three days' diligent 

 search he found only twelve living examples" (Baldwin). 



Subgenus CYCLAMASTRA Pilsbry & Vanatta. 



Cydamastra PILS. & VAN., Proc. A. N. S. Phila., 1905, p. 

 570 ; type A. cyclostoma Bald. 



The shell is deeply umbilicate in all post-embryonic stages, 

 varying in shape from biconic, somewhat Heliciform, to glo- 

 bose-conic or ovate-conic, the last whorl angular or rotund. 

 Embryonic whorls with faint radial ripples or nearly smooth ; 

 later whorls brown under a thin brown or yellowish cuticle. 

 Type A. cyclostoma Bald. 



Cydamastra occurs on all of the Hawaiian Islands except 

 Niihau, Lanai and Hawaii. The open axis is evidently an 

 old feature, characteristic of the neanic stage in Kauaia, etc. 

 Nearly half of the known species are found only as fossils. 

 The genera Pterodiscus, Planamastra and Armsia evidently 

 had their source in Cyclamastra. 



Series of A. split/erica. 



Besides the following species, this group includes A. obesa 

 and A. agglutinans (carinata) of the island of Maui. 



3. A. CYCLOSTOMA Baldwin. PL 15, figs. 1, 2, 3, 6. 



The shell is umbilicate, conic above, convex below tfoe 

 strong median peripheral carina ; moderately solid ; purplish- 



