LOWER PALAEOZOIC GASTEROPODA — ETHERIDGE. 
73 
Genus Mourlonia, De Koninck , 1883. 
(Faune Calc. Carb. Belgique, 1880, pt. 4, p. 75.) 
Mourlonia duni, sp. nov. 
PI. xv., Fig. 5 ; PI. xvi., Fig. 2. 
Sp. char. — Shell conical, or somewhat trochiform, the sides of 
the cone fairly continuous; spire rather depressed, but acute at the 
apex ; whorls six, gently rounded ; base convex. Body whorl 
large, more than twice the height of the penultimate whorl, 
obtusely angular at the centre ; sutures faintly impressed ; band 
sutural on all but the body whorl, bounded above by a faint keel, 
on the body whorl occupying the obtuse median angle, the bound- 
ing keels very sharp and distinct, with a faintly impressed groove 
below the lower, and apparently without special sculpture ; sinus 
unknown ; umbilicus open, although not widely so ; mouth oval, 
with the inner lip reflected somewhat over the umbilicus, but 
without concealing it. 
Obs. — The late Mr. Felix Ratte figured* three univalves from 
our Lower Palaeozoic rocks without assigning specific names to 
them, nor even generic in the case of two. Whether or no the 
present shell be one of these I am in doubt, but in some points 
his fig. 6 is like it, and again in other respects widely divergent ; 
for instance in the figure quoted there is too great a convexity of 
the whorls, too elevated a spire, and too prominent a band. At 
the same time there is the possibility that the two may be identical, 
allowing for defective drawing. 
Mourlonia duni is an exceedingly characteristic species of the 
Wellington Caves Limestone, and is at present unknown to me 
from any other horizon. It is named in honour of my former 
Assistant, Mr. W. S. Dun, to whom I am indebted for much 
cordial help. 
Loc and Horizon — Wellington Caves, 1ST. S. Wales. Siluro- 
Devonian. 
Genus Helicotoma, Salter , 1859. 
(Canadian Organic Remains, 1859, Dec. I., p. 10.) 
Helicotoma joiinstoni, sp. nov. 
PI. xv., Figs. 6 — 8 ; PI. xvi., Figs. 3 and 4. 
Straparollus ( Maclurea) tasmanicus , Johnston, Geol. Tas., 1888, 
t. 5, f. 7 (excl. f. 1 and la). 
Sp. char. — Shell discoid, of about four whorls, each nearly 
twice the breadth of the preceding ; spire short, wholly depressed 
* Proc. Linn. Soc. 1ST. S. Wales, x., 1, 1885, t. 9. f. G. 
