the apex hexagonal in section, the angles rather sharp and a little projecting, intervals nearly- 

 flat. Not far from the apex a secondary riblet arises in each of the two faces on the outer 

 curve, and somewhat later the lateral faces and those on the concave side are similarly divided ; 

 the secondary riblets gaining rapidly in strength, and on the latter part of the shell equal to 

 the six primary ribs. Toward the aperture there are 12 equal, equidistant ribs, rounded but 

 well projecting, and about half as wide as the concave, excavated intervals, which are smooth 

 except for light growth striae. Aperture circular, the outer edge of peristome scalloped by the 

 ribs. Apical orifice circular, about half as wide as the truncated apex. Length 19, diam. at 

 aperture 2,25, at apex 0,9 mill. 



Diagnosis of an older specimen. Shell soiled or Isabella-whitish, moderately 

 arcuate, the curvature mainly posterior. Sculpture : at and near the apex with 7 strong, rounded 

 ribs separated by deeply concave and decidedly wider intervals; passing anteriorly the ribs 

 become lower and wider, and tend to split by the appearance of progressively deepening sulci 

 on their side slopes, so that at the aperture there are about 10 very low ribs of unequal 

 prominence, besides some incipient ones; the intervals shallow and narrower than the ribs. 

 Growth striae fine and rather inconspicuous throughout, no longitudinal striation. Aperture sub- 

 circular retaining a slightly hexagonal form, as long as wide; apex rather large, the orifice 

 small, oval, longer than wide, with thick walls; no slit or notch. Length 19, diam. at aperture 

 2,8, at apex 1,3 mill. 



Distribution. China Seas (North Pacif. Expl. Exp.); St. Vincent and Spencer Gulfs, 

 Investigator Strait, and Backstairs Passage (Verco). 



Remarks. Mr. Jos. C. Verco has published the following interesting note on this species : 



"Angas misidentified our shell from Henley Beach as D. octogotttuii Lam., and cited it 

 as a South Australian shell in P. Z. S., 1878, p. 868. Pilsbry & Sh.\rp, in Tryon's Man. of 

 Conch., vol. XVII, p. 248, described a shell under the name of D. Bednalli, from St. Vincent 

 Gulf, sent to them by Mr VV. T. Bedn.a.ll. This nam.e would stand, were it not that specimens 

 of our extremely variable species are inseparable from D. intercalatuDi Gould, 1859, which 

 has priority. 



I have examined more than three hundred individuals, dredged by me in St. Vincent 

 and Spencer Gulfs, Investigator Strait, and Backstairs Passage. They have been taken alive at 

 all depths between eight and twenty-two fathoms, chiefly in muddy bottoms. I have vainly 

 endeavoured to discover more than one species among them. They are exceedingly variable, 

 and were it not for intermediate forms, quite a dozen species might be created. 



Its length varies of course : firstly, with its age ; individuals when very young are only 

 5 millimetres, when senile 37; secondly, with the amount of its posterior end which has been 

 removed, so that a stouter, older shell may not be so long as another which is evidently 

 younger and has not suffered so much truncation. 



Its curvature is also very variable. In its early stage of growth it is well curved, but 

 becomes gradually, though markedly, le.ss so as it gets older. Since the posterior end is progres- 



