18 SYSTEMATIC ARRANGEMENT 



acute lobe on each side, and a single elongated filament behind. 

 Teeth 1 • 1 • 1 . Operculum ovate, triangular, acute, with two longi- 

 tudinal folds ; apex acute, membranaceous, with a notch on the outer 

 or left side; nucleus subapical, on a level with the notch. — Adams, 

 Gen. Moll. t. 12. f. 5. 



1. P. senticosum, Quoy, Voy. Ast. t. f. 



2. P. textum, Adams, Gen. Moll. t. 12. f. 5. 



The operculum of Phos senticosum is on the back of the expanded 

 foot, as in the animal of most of the Nassce, which it altogether 

 resembles, except that the hinder extremity (of the foot) is serrated, 

 and has one tail instead of two as in Nassa. I never saw it use its 

 operculum when walking. — Trail, MSS. 1853. 



19. Cyllene. 



Shell ovate or obconic ; spire conic, short, with a deep sharp-edged 

 groove on the suture ; mouth ovate. Operculum ovate, lanceolate, 

 with an oblique central groove ; apex acute ; nucleus apical ; outer 

 edge smooth. Animal ? Teeth ? 



I. C. Owenii, Gray, in Beechey Voy. 108. 



20. NORTHIA. 



Shell turrited ; spire acute ; mouth ovate ; inner lip thin, smooth, 

 with a sharp keel over the canal ; outer lip crenated, toothed. Oper- 

 culum ovate, elongate ; apex slightly curved, with a notch on the 

 outer side. — Adams, Gen. Moll. t. 12. f. 1 a, b. Teeth ? 



1 . N. pristis, t. 84 a. f. 4. 



Northia is found at low-water mark at Panama ; the outer lip of 

 old shells is much thickened. — C. B. Adams, 295. 



The account of the operculum is on the authority of the specimen 

 figured by Mr. Adams ; the specimen in the British Museum has 

 an oblong operculum, with an elongated nucleus on the front of the 

 outer side, like Buccinum ; but perhaps it is surreptitious. 



Fam. III. BUCCINIDiE. 



Head truncated. Tentacles moderate. Mantle enclosed. Oper- 

 culum horny, annular, oblong ; nucleus on the outer edge. 

 Shell external ; pillar smooth or concave. 



A. Operculum oblong ; nucleus elongate, occupying the long outer 

 edge (fig. 10). 



a. Rapanina. Siphon produced ; canal of shell rather elongate, 

 bent up at the end. 



1. Rapana. 

 Shell subglobose or top-shaped ; spire short ; whorls lamellar, 



