150 AMASTRA, KAUAI. 



Amastrella, occurring on all the islands except Lanai and 

 Hawaii. It is a primitive group, by its smooth apex, small, 

 oblique columellar fold and open axis. 



Its wide distribution may be taken as evidence for a con- 

 siderable antiquity. Moreover, four or five of the seven 

 species known are extinct, mainly occurring in deposits more 

 or less remote from the habitats of living Amastrse. We have 

 to do, therefore, with an ancient group, now on the verge of 

 extinction. The species are as follows: 



Kauai : A. similaris. 



Oahu: A. extincta, hartmani, sola, antiqua. 



Molokai : A. umbilicata. 



Maui : A. morticina. 



A. antiqua is a rather large, solid, thick-lipped form; A. 

 sola has the verge of the umbilicus and the basal lip rounded. 

 A. extincta is not certainly known to belong to this group. 

 The other species are extremely similar, having the verge of 

 the umbilicus and the base of the aperture subangular ; and, 

 except for their geographic separation, they might almost be 

 considered forms of one species. 



5. A. SIMILARIS Pease. PI. 15, figs. 7, 13, 14. 



The shell is umbilicate, ovate-conic, rather solid, with fine 

 but rather rough and unequal striation on the last whorl. 

 Spire straightly conic, of 5% rather convex whorls. The em- 

 bryonic whorls are convex and smooth. The last whorl is 

 compressed around the umbilicus, spirally guttered within it. 

 The aperture is angular at both ends. The outer lip is ob- 

 tuse, a little thickened within. Golumella straight, forming 

 an angle with the basal lip, and bearing a retreating, ob- 

 lique fold near the base. Umbilicus well-like, very deep. 



Length 12.5, diam. 7.7, length of aperture 6.25 mm. 



Length 12.2, diam. 7, length of aperture 6 mm. 



Kauai, fossil (Pease) ; Waimea (Pse., in coll.) ; Mana 

 (Baldwin). 



Amastra rugulosa Pease var. similaris PEASE, Journ. de 

 Oonchyl., xviii, 1870, p. 96. Achatmella similaris BALDWIN, 

 Catalogue, 1893, p. 10. 



