Phacusso.] GASTROPODA. 627 



base. Epidermis thin, not shining. Spire, broadly conoidal, convex, 

 the height not quite equal to that of the aperture. Protoconch of 

 1 smooth whorls, flattened. Whorls 5|, slightly convex, the last not 

 descending, regularly rounded at the periphery ; base convex. Suture 

 impressed. Aperture a little, oblique, broadly lunar. Peristome simple, 

 straight, acute, regularly arched. Columella short, oblique, arcuate. 

 Inner lip reflexed above. Umbiliriix narrow, deep, open, very little 

 hidden by the columellar reflexion. 



Diameter Maj., 6-5 mm. ; min., 6mm. : height, 3-3 mm. (type). 



Dentition (Suter, T.N.Z.I., xxiv, 286, pi. 20, f. 2-4). It does not 

 differ much from that of the type species. 



Jaw strongly arcuated, with about 40 to 45 vertical plaits, indenting 

 both margins. 



Type in the British Museum. 



Hnb. North Island : Auckland (H. S.) ; Waimarama (A. Hamil- 

 ton) ; Hawke's Bay (Colenso) ; Dannevirke (Brooks) ; Rusthall. 

 Wanganui (R. Murdoch) ; Wellington (T. W. Kirk). South Island : 

 Kenepuru (McMahon) ; Nelson ; Kowai Bush (Professor Chilton) ; 

 near Eeefton (Cavell) ; Hooker Valley (H. S.) ; west of Mount Cook 

 (Filhol) ; Fortrose (Miss Rich) ; Bealey ; Dunedin. 



lli'Hiftrks. Albinos are sometimes found ; they are yellowish- 

 white, without any colour-markings. 



Genus 2. THALASSOHELIX, Pilsbry, 18'.i2. 



Thalassohelix, Pilsbry, " Nautilus," vi, Sept. 1892, No. 5, 56. Type : Hdi.r 

 zelandice, Gray. "Thalassia of Hutton and other New Zealand authors; 

 not Thalassia, Albers, 1860 ; not Thalassia, Chevrolat, 1834, a genus of 

 Coleoptera. Thalassohelix, Pils., Man. Conch. (2), ix, 12. 



Animal with narrow foot bearing a caudal mucous gland with a 

 papilla above it ; mantle slightly reflected over the peristome. 



Jaw arcuate, with flat plaits. 



Dentition : Central tooth with a short mesocone, the ectocones 

 obsolete ; laterals with a short ectocone, which disappears on the 

 marginals, leaving a long oblique mesocone only. 



Shell umbilicated, rarely imperforate, thin, depressed or trochiform, 

 the periphery acutely keeled, bluntly angled, or rounded ; apical 

 whorls most minutely spirally striated or smooth ; aperture rather 

 large ; lip thin, simple, subreflexed at columella. 



Distribution. New Zealand and Tasmania. ; perhaps also Aus- 

 tralia. 



Remarks. The dentition resembles Phacussa in the prominence of 

 the mesocones and obsolescence of ectoccnes on the marginal teeth, 

 and this peculiarity also serves to distinguish Thalassohelix from 

 Therasia, the shell of which is of a similar form. 



