218 TORNATELL1DES OF HAWAIIAN ISLANDS. 



usually it is slightly stronger in the adult stage. The colu- 

 mella is usually unarmed in adult specimens. In immature 

 specimens the columella is furnished with two oblique parallel 

 lamellae or folds, of which the lower is usually much stronger 

 than the upper; the latter being situated high, close to the 

 parietal wall. 



This group is easily distinguished by its flat whorls. The 

 form is more slender than is usual in the genus Tornatellaria. 



a. Surface sculptured with irregular, low, rib-striae. 



T. insignis, no. 26. 

 a 1 . Surface smooth. 



b. Parietal lamella of adults moderately developed, 

 more than 0.18 mm. in height. 



c. Parietal lamella of adults more than 0.25 mm. 

 in heights ; shells with 7 or more whorls. 

 d. Adult shells more than 4 mm. in length. 



T. attenuatus, no. 25. 



d 1 . Adult shells less than 3.3 mm. in length. 



T. pilsbryi, no. 27. 



c 1 . Parietal lamella of adults less than 0.22 mm. in 

 height, shells with less than 6% whorls. 



T. cyphostyla, no. 24. 



6 1 . Parietal lamella of adults very low, less than 0.1 mm. 

 in height. 



c. Length 2.9, diam. 1.5 mm. Oahu. 



T. oahuensis, no. 28. 

 c 1 . Length 4.6, diam. 2.2 mm. Molokai. 



T. moomomiensis, no. 29. 

 24. T. CYPHOSTYLA (Ancey). PL 48, figs. 1, 2. 



"Shell conoid-oblong, slender, smooth, white in the sub- 

 fossil condition, thin, glossy, openly but minutely perforate. 

 Spire conic, long, the sides straight, summit obtuse. Whorls 

 6, slightly convex, regularly increasing, separated by a linear, 

 appressed suture, the last oblong, somewhat tapering. Aper- 

 ture distinctly oblique, truncate-oval, armed with a single re- 

 volving parietal lamella. Columella regularly arcuate-slop- 

 ing, somewhat thickened, unarmed. Peristome simple, acute, 



