158 AMERICAN JOURNAL 



with doubt to genus Pterocyclos, in Am. Jour. Conch. 1865. 

 Having discovered a second species which agrees with the first 

 in general shape and operculum, we do not hesitate to distinguish 

 them by a separate generic name. It differs from Pterocyclos 

 in the shape of its aperture and lip, which are continuous and 

 simple. The operculum is reflected and expanded at base into 

 a broad disc. No species of Pterocyclos inhabit Polynesia. 

 They are mostly confined to India and Ceylon. The nearest 

 locality is that of Borneo. The above genus is apparently con- 

 fined to the southern extremity of Polynesia. 



D. parva, Pse. 



1865. Pterocyclos ? parva, Pse., Am. Jour, of Conch, p. 290. 



1866. " " " " " " pi. 5, fig. 8. 



Hab. — Insl. Aitutake, Hervey. 

 Operculum, Plate 12, fig. 12, (1868). 



D. rotella, Pse. Plate 12, fig. 13. 



Description. — T. turbinata, solida, umbilicata; laevigata; spira 

 elevata; anfr. 4, rotundato-convexis ; ultimo ad peripheriam 

 rotundatus ; sutura bene impressa ; perist vix adnatum ; pallide 

 spadicea, ad peripheriam fascia albida cingulata. 



Dimensions. — Diam. 2J, alt. 2 mill. 



Hab. — Insl. Atiu. 



Shell turbinate, solid, umbilicate, smooth, of a pale brown 

 color, encircled at periphery with a whitish band ; spire ele- 

 vated ; whorls 4, roundly convex ; the last rounded at periphery ; 

 suture Avell impressed ; peristome slightly attached. 



