ARMSIA, AMASTRA. 133 



been diversely differentiated, and probably represents a 

 parallel phylum derived from the same Amastrine stock be- 

 fore the spire had become flat. 



This genus is dedicated to Mrs. J. M. Arms Sheldon whose 

 assistance has enabled us to illustrate the Achatinellidae 

 more fully than would otherwise have been possible. 



1. A. PETASUS (Ancey). PI. 24, figs. 3, 4, 5, 6. 



"Shell very broadly and perspectively umbilicate, sub- 

 lenticular, thin, buff-brown, uniform, slightly shining, rudely 

 and closely rugose-striate, the stria? lamellose. Spire broadly 

 conoidal, the sides somewhat concave, summit projecting a 

 little, rather obtuse. Whorls 5, nearly flat, separated by a 

 linear and not very deep suture, regularly increasing, the last 

 provided with an acute carina above and another below around 

 the umbilicus, hardly descending, somewhat sloping above, 

 inversely conic and flat below the principal carina. Umbili- 

 cus saucer-shaped, conic. Aperture nearly vertical, ax- 

 shaped, acutely angular on the right, more obtusely below, 

 toothless. Peristome simple, unexpanded, the margins re- 

 mote. Alt. 2.2, diam. maj. 4.33, min. 3.75 mm." (Ancey). 



Oahu: Waianae Mountains (Baldwin). 



Pterodiscus petasus ANCEY, Proc. Malac. Soc. London iii, 

 July, 1899, p. 268, pi. 12, f. 4. PILS. & VAN., Proc. A. N. S. 

 Phila. 1905, p. 574, pi. 38, f. 7, 8. 



Easily known by its bicarinate body-whorl, low-conic spire 

 and very broadly conic umbilicus. The shell described and fig- 

 ured by Mr. Ancey (fig. 6) was not mature. Adult shells have 

 the outer, basal and columellar margins of the lip broadly ex- 

 panded, the revolving angles of the last whorl becoming ob- 

 solete upon it. The last third or fourth of the last whorl 

 descends rather deeply. Shells measure from alt. 3, diam. 4.8 

 mm. to alt. 3.5, diam. 5.8 mm. 



Genus AMASTRA H. & A. Adams. 



Amastra ADS., Genera of Recent Mollusca, ii, p. 137 (Feb., 

 1855). PEASE, P. Z. S. 1869, p. 649. GULICK, P. Z. S. 1873, 

 p. 91, type A. magna. 



