AMASTRA, HAWAII. 311 



Hawaii: Mana, Hamakua district, fossil (II. W. Henshaw). 



Amastra (Laminella) sinistrorsa BALDWIN, Nautilus, xix, 

 April, 1906, p. 138. HENSHAW, Journ. of Malac., xi, p. 63. 



This apparently extinct species from the Holocene deposits 

 of the Hamakua district, is the only member of its group 

 found on Hawaii. It is more slender than the Mauian A. 

 hutchinsonii, and differs by its carinate embryonic whorls 

 and less coarse sculpture. Described and figured from the 

 type specimen, kindly lent by Mr. Baldwin. Another shell 

 of the original lot is slightly broader. Like all the shells of 

 the Mana deposits, it has lost all color and cuticle. 



Section AMASTRELLA Sykes (p. 151). 



Series of A. melanosis. 



By the cuticle and striate apex, A. melanosis and its allies 

 are very similar to Oahuan Amastrellas of the inflata group. 

 Other species, such as A. senilis and fossilis have the umbil- 

 icus of Cydamastra, but differ from that group by the sculp- 

 tured embryonic whorls. While the group is a natural series, 

 its species are rather diverse, indicating long isolation of a 

 stock derived from rather generalized ancestors. Northern 

 Hawaii, by its mature topography and the great cliff gnawed 

 by the waves, may be as old as any of the islands; and its 

 Amastrellse were no doubt due to an early radiation of these 

 primitive Amastrae. 



105. A. SENILIS Baldwin. PI. 47, fig. 5. 



The shell is openly umbilicate, broadly conic, thin. Spire 

 conic with nearly straight outlines, the apex subacute, em- 

 bryonic whorls closely, finely and sharply striate; following 

 whorls moderately convex, roughly marked with growth- 

 wrinkles, the last three whorls sometimes showing small, very 

 shallow spiral istrige, the last whorl carinate at the periphery 

 in front, coarsely malleated, producing irregular, spiral, de- 

 scending ridges between the flattened facets. The columella 

 is dilated above, vertical, and bears a small fold. The um- 

 bilicus is cylindric and deep, 2 mm. wide. 



Length 21.2, diam. 16, aperture 11.1 mm.; 6% whorls. 



