208 
MEMOIRS OF THE QUEENSLAND MUSEUM. 
forms is of particular interest since both are from Cretaceous beds — Dinocochlea 
from the early part of the period and the new form apparently from near the middle. 
Origin. — In attempting to explain the origin of such a spiral object it is 
necessary to summarise and to stress the following points : — 
1 . The structure is a relatively uniform helicoid spiral with no regular 
increase or diminution in size of whorls, 
2. One end is bulbous suggesting that the structure was closed at that 
point. Unfortunately, the opposite end is not preserved. 
3. No trace of an investing shell is to be found on the surface of 
the specimen or on the impressed zone between the whorls. 
4. The object lay more or less in the plane of bedding in lacustrine 
or estuarine sediments of Cretaceous age. 
5. The material of which it is composed is an arenaceous rock type 
common to Cretaceous sediments in the Great Artesian Basin. 
Considering the great bulk of the specimen, the last of these premises 
suggests that the structure was formed either by concretionary action within 
an ordinary rock type or else by the infilling of a spiral cavity existing at the 
time of deposition of the beds. 
The absence of any investing shell is important. In the marine beds of 
the Great Artesian Basin molluscs and other forms are very well preserved, 
and even with thin-shelled species it is rare to find an internal mould devoid 
of some traces of the shell. The fact that over the whole great surface of 
this spiral and in the impressed zone between the whorls there is no trace 
of any shell substance, renders improbable a suggestion that the specimen is 
an internal mould of an organism with a calcareous test. 
As possible explanations of similar, large, spiral structures previously 
described, the following suggestions have been made by various authors : — 
(A) An Inorganic Origin — 
1. Infillings of potholes. 
2. Concretions. 
(B) An Organic Origin — 
3. Internal moulds of Gastropods. 
4. Coprolites. 
5. Burrows. 
6. Roots. 
As Woodward (1922 p. 242) has pointed out for Dinocochlea the 
horizontal position of the specimen makes the suggestion of an infilled pothole 
untenable. 
If it were possible to record a process producing horizontal, spiral 
structures in a concretionary way such an action would be the most favourable 
explanation of the origin of this form. Like Dinocochlea it occurs in a sedi- 
mentarv series notably rich in concretions. As mentioned previously the 
