& /] 
THE GEELONG NATURALIST. 4 
NOTES ON TWO RECENTLY DESCRIBED FOSSILS 
FROM GEELONG. 
Bv T. S. Harr. 
The two fossils which I have recently described, from the 
neighborhood of Geelong, present several points of interest, a 
few of which I shall take this opportunity of pointing out. 
The fossils belong to two new genera of the family Stylas- 
teridae; Sub-order, Hydrocoralline ; Order, Hydroida; Class, 
Coelenterata. 
Th commonest and best-known member of the Order is the 
little freshwater Hydra itself. This may be seen figured in 
most works on Zoology, and is to be found in almost every pond. 
Hydra has a tubular body, with a ring of tentacles round a 
mouth which occupies one end of the tube, aud that is pretty 
nearly all there is of it. It is a solitary animal, but some of its 
near allies grow in what are termed colonies. Their bodies are 
united, and the digestive cavities of all open into one tube or its 
branches; so that whatever one eats serves as nutriment to the 
whole colony. Hydra is “naked,” that is it has no external 
skeleton: Many forms develop a horny supporting external 
sheath, as, for instance, Plumularia, Sertularia, etc. They are 
common marine forms, and frequently grow over seaweed. The 
skeletons of some closely resemble those of some polyzoa, though 
there is no relationship between them. One group alone, the 
Sub-order Hydrocoralling, secretes a calcareous skeleton. 
In some of the * colonial" groups above mentioned there is 
specialization of certain zooids to perform certain functions. 
Thus some will do all the eating for the colony; others will 
catch the prey, and others will perform the functions of repro- 
duction, some being males and others females. The ones that 
catch the prey are called sometimes “ fighting zooids," and are 
provided with clusters of thread-cells. These are small drum- 
_ like cells, in each of which is coiled up a long thread with a 
spear-like head. When the drum is touched or the animal irri- 
tated, the cell bursts and the thread shoots out, stings what it 
touches, and if it be a microscopic animal, killsit. The stinging . 
red jelly-fish, so common in the baths at certain seasons, are 
provided with these thread-cells, which as most of you are 
doubtless aware, have the power of penetrating the human skin, 
and irritating it very considerably. 
In the Hydrocorallins then we have a colonial form, that is 
one which is composed of a colony of zooids, organically con- 
nected with one another, and sharing nutriment in common. 
The Zooids are of three forms—(1) Gastrozooids or nutritive 
zooids; (2) Dactylozooids, or fighting zooids, which catch food 
and pass it over to Number 1; (3) Gonozooids, or those in which 
e 
