118 GASTROPODA. \Aspidobranchia. 



globose, not eroded in front of the aperture ; base slightly convex 

 or flat. Suture impressed. Aperture oblique, nacreous and smooth 

 within. Outer Up regularly convex, sharp, bordered by a narrow 

 yellow or white followed by a black strip. Columella oblique, short, 

 nearly straight, with 1 or 2 tubercles, white, dilated upon the parietal 

 wall, but not extending to the upper lip. Umbilical tract slightly 

 pitted, subconcave, no pearly band. 



Diameter, 16 mm. ; height, 15 mm. 



Dentition unknown. 



Type in the British Museum. 



Hob. On mud-flats of the South Island ; Heathcote Estuary, 

 near Christchurch (H. S.) ; Dunedin (Captain Hutton). Brought to 

 England by Captain Cook. 



Remark. Pilsbry wrote to me in 1897 : ' Your New Zealand 

 species will stand as M. corrosa, A. Ad. It is perfectly distinct from 

 the West and South Australian M. melanoloma. Of course, my descrip- 

 tion and figures refer to corrosa, for at that time I had not seen the 

 true Australian melanoloma." 



Fossil in the Pliocene. 



Subsp. undulosa, A. Adams, 1853. 



CJdorostoma undulosum, A. Ad., P.Z.S., 1851 (1853), 182. Monodonta cor- 

 rosa, subsp. imdulosa. A. Ad., Man. Conch. (1). xi, 105, pi. 22. f. 45-47 ; 

 Stiter, P. Mai. S., ii, 267. Trochus undulosus, A. Ad., Ereb. & Ter., 4, 

 pi. 1, f. 15. T. attritus, Hombr. & Jacq., Voy. P.S., 57, pi. 14. f. 19. 20. 

 Labio Hectori, Hutt., C.M.M., 37. Diloma Hectori, Hutt., M.N.Z.M., 95. 



Larger than the species, and the spiral sculpture more distinct. 

 Colour yellowish, with undulating lines of dark purple. Aperture 

 sometimes faintly lirate within. 



Diameter, 20-22 mm. ; height, 17-18 mm. : 19 mm. by 16 mm. 

 (type). 



Dentition unknown. 



Type in the British Museum. 



Hob. From Sumner to Dunedin ; on rocks, not common. 



Subsp. plumbea, Hutton, 1883. Plate 38, fig. 8. 



Diloma plumbea, Hntt., T. N.Z.I., xv, 126. Monodonta melanoloma, Menke, 

 subsp. plumbea, Hutt., Man. Conch. (1), xi, 105, pi. 20, f. 15-17; Suter, 

 P. Mai. S., ii, 267. 



Shell globose-conic,' imperforate, solid. Sculpture consists of obso- 

 lete coarse lirae on the last whorl only. Colour dull purplish, spire 

 usually eroded, white. Spire conical, acute. Whorls 4 to 5, flatly 

 convex ; base flat. Suture superficial. Aperture as in the species, 

 but the outer lip margined within only by black. Inner lip spreading 

 broadly over the lower part of the parietal wall and umbilical tract, 

 bordered outside by black ; no pearly band. 



Diameter, 16 mm. ; height, 14-5 mm. 



Dentition.^ Hutton, T.N.Z.I., xv, pi. 15, f. E. 



