From the Upper Yarra District. 223 
Bryozoa or Moss Corals.—These creatures occupy a 
higher position in the organic scale than the simpler-formed 
polypes with which they were formerly associated. Many 
hundreds of microscopic fossil species have been discovered 
within the last few years. The shells, or outer tunics, enter 
into the composition of chalk beds, compact limestone, and 
sea sand, as well as the sands of the deserts. These fossil 
forms, many species of which are still living, are mostly 
microscopic ; those which are visible resemble minute grains. 
Those which at present engage our attention belong to the 
genus Celaria, and, I am of opinion, are closely allied to 
C. Loricata. 
A second species of Bryozoa, which, however, I am unable 
to distinguish, also occurs in company with those mentioned. 
This variety forms rounded columns, about an eighth of an 
inch in length, with fine ribs or threads passing longitudinally 
downwards. 
The few forms which I have been able to detect in the 
. Specimens forwarded to me lead me to the conclusion, that 
the strata in which they occur belong either to the uppermost 
cambrian or to the lowest silurian formation. It is highly 
remarkable that these rocks are found in an auriferous locality, 
and in the immediate vicinity of our earliest gold-field. 
I may beg to observe, that fossil remains of the oldest 
Neptunic era may be obtained in abundance at certain 
spots in an extensive line of district eastward of Mel- 
bourne, and which would well repay the trouble of the en- 
terprising man who would institute a search for them. 
Subsequently to writing the above, I have discovered by 
‘a minute examination, in the rocks referred to, the forms 
exhibited in the plate. The paleontological description of 
these will form the subject of another paper. 
Art. XVIII.—Practical Remarks on Hydrometry. By 
CiementT Hopexinson, Esa. C. E. 
THE contradictory results of the hydrometrical observations 
made by different persons in this colony, had induced me, 
some weeks ago, to give notice of my intention to submit to_ 
this society a paper embodying my objections to the mode of 
guaging streams often adopted by the engineering profession, 
and the result of my own experience in these operations. 
Recent domestic afflictions had, however, caused me totally 
