TORNATELLIDES OF HAWAIIAN ISLANDS. 231 



two lamellae or folds. In adult specimens the upper columellar 

 lamella is the stronger; sometimes the lower or both lamellae 

 are obsolete. The opposite occurs in immature specimens, as 

 the lower lamella is usually much stronger than the upper, 

 sometimes extending horizontally for about l /^ the diameter of 

 the aperture. The umbilicus is rather small, oval in outline. 

 In immature specimens the parietal lamella is much stronger 

 than in adults. The embryonic whorls may be spirally striated 

 or not. 



This is one of the most numerous groups in species and 

 varieties. It differs from the Group of T. simplex by having 

 two distinctly developed columellar lamella in the neanic stage. 

 These may persist in the adult stage in some species ; in others 

 they are more or less receding or immersed, or none may be 

 visible in the adult, which by itself might cause such species to 

 be placed in the simplex group. 



a. Adult shells with the parietal lamella less than 0.05 mm. in 

 height ; columella unarmed ; 2.1 x 1.1 mm. 



T. leptospira, no. 48. 



a\ Adult shells with the parietal lamella more than 0.1 mm. 

 in height. 



b. Adult shells less than 3.1 mm. in length. 



c. Whorls very closely coiled; 6 or more whorls. 

 d. Umbilicus rather small, but more than 

 0.24 mm. in diameter. 



e. Adult shells less than 2.7 mm. in 

 length. 



/. Adult shells with the diameter 

 less than 52% of the length. 



T. brunneus, no. 43. 

 /*. Adult shells with the diameter 

 less than 48% of the length. 



T. pyramidatus, no. 41. 

 c l . Adult shells 2.9 mm. or more in 

 length. 



/. Light brown ; upper columel- 

 lar lamella conspicuously 

 emerging in adults. 



