Palceontology of Older Tertiary of Victoria. 103 



that of the intervening space, the ratio being about one to two. 

 Earlier spire whorls costate, the first bearing about seven costae, 

 which are strongest medially, thinning out towards the posterior 

 suture and also on the anterior slope. The costfe on the succeed- 

 ing whorls gradually become less distinct till their position is 

 only discernable by a slight angulation of the keel. 



Whorls encircled by strong spiral threads about twelve to 

 fourteen in number, two of these being more strongly developed 

 than the remainder, one margining the deeply excavated suture, 

 and thereby making the shell more angular at this region, while 

 the other forms the prominent and characteristic encircling keel. 



The spiral threads are broad and flattened, but narrower than 

 the intervening spaces, the latter occasionally but not regularly 

 showing a faint spiral thread or faint spiral striae. The remaining 

 ornament consists of very fine close-set lines of growth, which 

 are more distinct in the intervening spaces. 



Aperture ovate ; peristome very thin ; inner lip quite distinct 

 from the columella ; outer lip undulate, channelled interiorly 

 corresponding to the spiral threads, the latter projecting slightly 

 at the thin edge, the most marked projections being at the end 

 of the sutural and medial keels. Outer lip contracted so closely 

 to the columella as to give the aperture the appearance of being 

 entire, but really opening into a long slender slightly waved 

 canal, the opening of which is contracted to an extremely narrow 

 slit. The threads on the canal are narrower and more angled 

 than those on the spiral whorls. 



Dimensions. — Length of shell, .30 mm.; breadth, 7 mm.: 

 breadth of aperture, 2 mm.; length of aperture, 3 mm.; length 

 of canal, 10 nmi. The above dimensions are those of the type 

 specimen, but appear to be about the average of the specimens 

 yet obtained, with the exception of the imperfect example figured 

 on the accompanying plate, which is proportionately larger, the 

 breadth of its aperture being 2-5 mm., length or aperture, 3 -5 

 mm., and length of canal, 13-5 mm., the latter being much more 

 waved or bent than in the type. 



Locality. — Eocene clays of Balcombe's Bay, Mornington, and 

 Curlewis ; also from the Eocene beds of Muddy Creek, "Western 

 Victoria. 



