152 HELCIONISCUS. 



ous (43-45) strong rounded ribs, closely but usually rather super- 

 ficially cut by concentric striae. Color clear buff, unicolored or hav- 

 ing the ribs black or black-spotted. 



Interior white and silvery, the central callus of a more or less in- 

 tense purple- black. 



Length 61, breadth 51, alt. 34 mill. 



Length 50, breadth 41, alt. 30 mill. 



Habitat unknown. 



Distinguished at once by the unusual coloring of the interior, 

 and the sculpture of the outside. All of the specimens before me 

 have the upper portion of the cone eroded. In one the central 

 black callus is very thick. The ribs are alternately larger and 

 smaller. They are scarcely strongly enough represented in the fig- 

 ure. 



Specimens having black ribs possess also two short dark streaks 

 radiating from the forward angles of the " head-mark " as in P. 

 boninensis, with which species this is probably most nearly allied. 



H. ENNEAGONA Reeve. PI. 28, figs. 35, 36. 



Shell ovate, a little attenuated in front, depressed, rather thick, 

 obtuse at the apex, subattenuated and inclined, densely crenulately 

 ridged, peculiarly nine-sided, the three front areas narrow. Yellow- 

 ish, the nine areas diagonally reticulately streaked with deep purple. 

 Interior silvery, iridescent. (Reeve.) 



Habitat unknown. 



P. enneagona REEVE, Conch. Icon., f. 44. (Dec., 1854.) 



H. LIVESCENS Reeve. PI. 73, figs. 99, 100. 



Shell ovate, rather thin, depressly convex, rather sharply pointed 

 at the apex, radiately densely granulately striated, striae slightly 

 waved; apex rather anterior. Pellucid blue-green, rayed with 

 blackish-purple, rays sometimes broken up into opaque blotches. 

 Interior iridescent-silvery, more or less transparent. (Rve.) 



Mazatlan (Reeve.) 



P. livescens RVE., Conch. Icon., f. 75, 1855. 



A very delicate subpellucid greenish-blue shell, painted with dark 

 purple rays which show through into the interior. The sculpture 

 consists of numerous slightly waved granuled lines. (Eve.~) 



The locality given by Reeve is more than doubtful. It seems 

 near P. rota Gmel. 



