Architectonicn.] GASTROPODA. 317 



consisting of the convex smooth nucleus only. Whorls 5, regularly 

 increasing, flatly convex, the last keeled ; base flattish. Suture but 

 little impressed. Aperture subquadrangular. Peristome discontinuous, 

 sharp. Columella vertical, broadly rounded. Umbilicus small, deep. 



Diameter, 12 mm. ; height, 9 mm. 



Dentition. Troschel, Das Gebiss d. Schnecken, ii, 156, pi. 15, f. 5. 



Type in the Mus. Hist. Nat., Geneva. 



Hob. Whangarei Heads (C. Cooper) ; Mokohinau Group ; Hau- 

 raki Gulf (C. Mathews) ; Wellington (T. W. Kirk) ; Chatham Islands. 



Genus 2. HELIACUS, d'Orbigny, 1842. 



Heliacus, d'Orb., "Mollusca Cubana," ii, 1842, 68. Type: Solarium Heberti, 

 Desh. Torinia, Gray, 1840 and 1842 (list-name only). Teretropoma, 

 Rochebrune, 1881. 



Shell turbinately elevated, or in some instances planorbiform ; 

 umbilicus typically moderate to wide, perspective, its margins slightly 

 crenulated ; lip and columella simple. Operculum corneous, typically 

 conically elevated, externally spiral, of numerous volutions, margined 

 by projecting edges ; internal face smooth, bearing a spirally twisted 

 median projection. 



Distribution. World-wide, tropical and subtropical seas. 



Fossil. Tertiary. 



1. Heliacus variegatus, Gmelin, 1790. Plate 15, fig. 20. 



Trochus variegatus, Gmel., Syst. Nat., ed. xiii, 3575. Heliacus gyrus, 

 Meusch., Gronov., 323. Trochus areolus, Gmel., Syst. Nat., ed. xiii, 3575. 

 Heliacus perspectiviunculus, Dillwyn, Cat., ii, 783. H. tessellata, 

 Deshayes, Encycl. Meth., 1830, 160. Torinia variegata, Gmel., Man. 

 Conch. (1), ix, 16, pi. 5, f. 75-79. H. variegatus, Gm. : Suter, T.N.Z.I., 

 xxxix, 266. 



Shell small, depressed, radiately and spirally sculptured, solid. 

 Sculpture consisting of close and numerous cinguli, 5 on the upper 

 whorls, 10 on the body- whorl, that below the suture, at the periphery 

 and just below it, being the strongest ; they are cut up by fine oblique 

 radiate narrow sulci ; umbilicus margined by a stout and crenulate 

 cord. Colour radiating alternate stripes of white and brown. Spire 

 low, depressed conoidal, of the same height as the aperture ; outlines 

 moderately convex. Protoconch of 1 smooth whorl. Whorls 5, regu- 



\j o 



larly increasing, slopingly convex ; base slightly rounded. Suture in- 

 conspicuous. Aperture subcircular. Peristome on the outside crenu- 

 lated by spiral sculpture. Columella vertical, broad, with an outer 

 denticle produced by the medial rib of the umbilical wall. Umbilicus 

 moderately large, deep, perspective. 



Diameter, 13 mm. ; height, 7 mm. 



Animal unknown. 



Hob. Off Cuvier Island, in 37 fathoms (Captain Bollons). Red 

 Sea, Indian Ocean, Pacific Ocean. 



