T tin its.] GASTROPODA. 427 



outer side. Spire conical, variable in height, usually the same as 

 that of the aperture, or a little less. Protoconch pupoid, of 2 whorls, 

 the first smooth, the second axially costate. Whorls 6 to 7, first 

 slowly increasing, the last rather large, distinctly shouldered, and 

 keeled by the first spiral rib ; base contracted above the fasciole. 

 Suture impressed, uneven. Aperture slightly oblique, narrowly oval, 

 angled above, with a short open slightly recurved canal below. Outer 

 lip sharp, laciniate, crenate and lirate inside, the lirse sometimes lighter 

 in colour. ( 'ohniiella vertical, lightly concave, somewhat twisted and 

 tapering below. Inner Up extending somewhat beyond the pillar 

 and broadly over the parietal wall, much narrowed towards the base. 

 Operculum with the nucleus sublatefal. 



Diameter, 13-5 mm. ; height, 27 mm. (type). 



Dentition (Button. T.N.Z.T., xv, 121, pi. 13, f. 8). Central tooth 

 with 5 subequal cusps. 



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



Hob. North Island to Cook Strait, on rocks between tide-marks, 

 common. Tryon says that it occurs at the Cape of Good Hope, and it 

 appears also in Gribbons's " List of South African Mollusca," 1888. 



Subsp. albomarginata, Deshayes, 1839. Plate 45, fig. 21. 



Pii/-pui-<i nlboniftrginata, Desh., Rev. Zool. Soc. Cuv., 1839, 360 ; Deshayes, 

 in (luerin Mag. Zool., 1841, pi. 44; Man. Conch. (1), ii, 170, pi. .~>1, f. 121, 

 124 ; ('hall. Rep., xv, 173 ; T.N.Z.I., xvi, 222. Purpura tristix, Dunker, 

 V.Z.B.G. Wien, xvi, 1866, !lo ; Keise " Novara," Moll., 6, pi. 1, f. 4, 

 1867. Polytropa bironica, Button, .1. <le Conch., 1878,20; M.N.Z.M., 

 57, not of Anton. 



This subspecies is of the same size as the species ; the whorls 

 are less prominently shouldered and not keeled ; the conspicuous 

 spiral ribs are wanting, and are replaced by numerous dark-coloured 

 subequidistant spiral threads, the interstices of about the same width 

 as the threads and usually white ; the axial sculpture consists of 

 laciniate or smooth and oblique grcwth-lamellee, producing a rough or 

 sometimes quite smooth surface ; outer lip with a white margin, 

 almost always banded with brown and white. 



Dentition. Button, T.N.Z.I.. xv, 121, pi. 13. f. T. 



Type. Mus. Hist. Nat,, Paris (?). 



Hob. Abundant throughout the South Island, less common in 

 the North Island. 



Var. rutila, Suter, 1899. 



Purpura scobina, rviila, Suter, J. Mai., vii, 1899, 55. 



Differs from the typical form, in which the interior is brcwn or 

 blackish-brown, by having this part of the shell coloured orange or 

 brownish-orange, the columella fulvous, and the epidermis of the 

 shell light-brown or cinereous, Avith a hue of yellow. Sculpture and 

 size very variable. 



