74 
RECORDS OF THE AUSTRALIAN MUSEUM. 
below the level of the body whorl, which is traversed on its outer 
angle by a keel, without nodes, crenulations or echinations, but 
variable in its degree of prominence and acuteness, on the inner 
side of the keel the surface of the whorl slopes rapidly away to 
the suture, with immediately above it a second feeble obtuse keel; 
on the under side the surface of the body whorl is either gently 
rounded or flattened, but the inner whorls rounded only ; umbilicus 
telescopic, but most of the whorls visible ; back in no way concave 
beneath the keel of the body whorl, but rounded and broadening 
towards the mouth, the surface loosing much of its convexity. 
Mouth generally rounded, but slightly insinuated at the keel, and 
more so along the sutural margin, the upper margin, in other words, 
retreating towards the shallow 7 notch or insinuation referred to, 
and the lower edge advancing and insinuated. Sculpture of the 
upper surface consists of fine obliquely retreating lyrulafc on the 
inner half of each whorl, and similar advancing lyrulse on the 
outer half, giving a faintly V-shaped figure, but on the wide 
back these lyrulse become more directly transverse ; on the under 
surface the lyrulse describe a sigmoidal curve, becoming much 
coarser and sub-larninar towards the mouth, the sharpest portion 
of the curve being immediately above the suture at the obtuse 
feeble keel. 
Obs. — Under the name of Straparollus tasmanicus , I feel con- 
vinced Mr. R. M. Johnston lias included two perfectly distinct 
shells. His figs. 1 and la. represent a Raphistoma that may be 
known as Raphistoma tasmanicum , Johnston, sp., whilst fig. 7, 
the subject of the present remarks, appears to me to be a Helico- 
toma , and I therefore propose for it the name of H. johnstoni. 
The specimen now figured was received in a collection of fossils 
forwarded from the Tasmanian Museum. PI. xv., Fig. 6, repre- 
sents the upper side, corresponding to Johnston’s fig. 7, whilst 
our PI. xv., Fig. 7, is that of the under or umbilical side of the same 
specimen. I am puzzled how to distinguish this from another 
shell that Mr. Johnston has figured as Lituites , sp. indet.,* except 
that in the latter the transverse laminae are too coarse for the lines 
occurring on the under surface of II elicotoma johnstoni. 
In the faintly V-shaped outline of the sculpture on the upper 
side, the apex of the V is at the keel of the body whorl, producing 
a slight notch on the outer lip, after the manner of Helicotoma , 
without in anyway simulating a true sinus. This reflection of the 
sculpture lines and the presence of the notch distinguish this 
shell at once from Polytropis , He Koninck. 
Log . and Horizon. — Gordon River, West Tasmania. Gordon 
River Limestone, Lower Silurian. 
* Johnston — Geol. Tas., 1888, t. 5, f. 8 and 10. 
