Monodonta.] GASTROPODA. 115 



Shell imperforate, depressed, globose, solid, black. Sculpture con- 

 sists of numerous close spiral strise, sometimes nearly obsolete, crossed 

 by oblique growth-lines, which, are often strongly developed. Colour 

 bluish-black or black, beach-worn specimens reddish or brownish ; 

 no spots. Epidermis fairly thick and solid, shining in fresh specimens. 

 Spire short, conoidal to conical ; apex rounded or acute. Protoconch 

 consisting of 2 spirally striate and lightly pearly whorls, sometimes 

 reddish. Whorls 4 to 5, slightly convex, rapidly increasing, the last 

 usually depressed or subconcave below the suture ; base rounded, 

 eroded and iridescent in front of the aperture. Suture linear, margined 

 below by a strong cord. Aperture large, oblique, greenish iridescent, 

 and closely lirate. Outer lip convex, rather thin and sharp, bordered 

 within by an extremely narrow black margin, followed by a broad 

 opaque white band, sometimes brilliantly iridescent. Columella con- 

 cave, obsoletely subdentate below, very broad and flattened or ex- 

 cavated on the face, composed principally of an opaque white layer, 

 which also lines the base, but does not extend to the edge of the lip. 

 Parietal wall with a band of nacre, uniting the ends of the peristome, 

 bounded on the outside with light brown or white. 



Diameter, 17-24 mm. ; height, 15-26 mm. 



TEETH OF RADULA. 



Dentition. Troschel, Das Gebiss d. Schnecken, ii, 236, pi. 24, f. 2 ; 

 Suter, P. Mai. S., ii, 264, fig. in text (as porcifera, Watson). 



Type (?). 



Hob. Sumner, near Christchurch (H. S.) ; St. Clair, near Dunedin 

 (H. S.) ; Preservation Inlet ; Pitt's Island, near Stewart Island (C. 

 Traill) ; Chatham Island ; Auckland Islands (Captain Bollons). Also 

 west coast of South America. 



Sect. 2. NEODILOMA, P. Fischer, 1885. 



Neodiloma, Fisch., Man. de Conch., 820. Type: Trochus cethiops, Gmel. 

 Neodiloma, Fisch.., Man. Conch. (1), xi, 9, 98. 



Similar to Diloma, but without the parietal band of iridescent 

 nacre ; surface smooth, grooved, or lirate ; unicoloured, spotted, or 

 tessellated ; columella with one or two denticles at the base, or smooth. 



Australasia. 



