AURICULELLA, OAHU. 73 



The parietal wall is always furnished with a lamella. In 

 most species this lamella is rather high in front, then descends 

 rather rapidly, and is continued in back as a raised line. In 

 a single species (A. serrula) the parietal lamella is serrated, 

 with sharp, outward projecting spines. In a very few species 

 a basal palatal fold is present. This fold sometimes persists 

 in the adult stage, but usually disappears at about the time 

 the shell reaches maturity. Most of the species are either uni- 

 formly dextral or sinistral, but in a few the direction of coil 

 is indifferently dextral or sinistral, often among individuals 

 of the same colony. 



Key to Species of Oahu. 



I. Form ovate-conic, the oblique diameter about half the 

 length of the shell or more (rarely less, in which case the 

 shell is conspicuously opaque) ; whorls of the spire but 

 slightly convex; columella usually having one fold. 

 a. Columella having a distinct fold or lamella ; length 6 to 

 12 mm., with 5% whorls or more. GROUP OP A. 

 AURICULA. 



&. Shell thin, sinistral ; lip thin, not in the least thick- 

 ened outwardly or within; color in browns, not 

 yellow; 5y 2 -6y 2 whorls. diaphana, no. 1. 



& 1 . Shell opaque or with yellow coloring ; lip slightly or 

 very much thickened within ; more than 6 whorls. 

 Either dextral or sinistral. 



c. Outer lip "duplicate," accompanied by an ex- 

 ternal ridge or keel; a transverse tubercle at 

 the posterior angle of the aperture. 

 d. A rounded ridge behind lip ; very solid, nar- 

 rowly umbilicate, malleate, not glossy, 

 the oblique diameter a little less than half 

 the length. malleata, no. 9. 



d l . Lip-ridge angular; shell wider. 



e. Adult nearly or quite imperf orate. 



ambusta, no. 8. 

 e 1 . Distinctly umbilicate, glossy. 



pulchra, no. 7. 



