THE GEELONG NATURALIST. He 235 
small and pointed ; gills, ample, the outer one smaller. The Shell of 
trigonia is almost nacrous, and is seldom found in limestone, except 
in casts silicified. Casts have been found in some formations in which 
the animal itself with its gills have been preserved. It is said the 
trigonia is able to leap over a ledge four inches high, and by that 
means, often escapes from the boat into the sea ; they are supposed 
to be migratory, as dredging for them is very uncertain, though they 
abound in some parts of Sydney Harbour, and we also get them 
around our'own coasts. 
The fossil trigonias are very abundant at Spring Creek and 
Maud, there casts are also found in the Belmont deposit, and the 
limestone at Maud is full of them The two species shown are 
T. Tatei, a new species, &&d-named by Mr. Pritchard of Melbourne ; 
and T. Margaritacea, found at Barwon Heads, by the late Mr. 
J. Bracebridge Wilson. 
OBSERVATIONS ON SOME CRUSTACEAN SPECIES. 
———— 
Bx A. B. F. Wirsox. 
Ix the order Stomapoda, we have the locustor mantis shrimp, 
i 1) which is a very interesting species; it is so named 
on account of its resemblance, in outward appearance and habits, to 
the mantis insect. These crustaceans mostly inhabit deep waters, 
their habits, like the mantis insect, are very voracious. 
I am indebted to my friend, Mr. W. Johnston, for a very fine 
specimen, which was caught just outside Hopetoun Channel in May, 
this year, 95, in about twenty-three feet of water, one or two have 
occasionally been caught in our bay (Corio) but they were never 
known to appear near Hopetoun Channel or in our bay in large 
numbers till June this year, when a great number of them were caught. 
The specimen I have measures 63 inches from head to tail ; 
from the tips of the antenne to the tail 8 inches, and across the 
carapace li inch. The body is somewhat flattened and divided 
into three lobes, the abdomen is long and jointed, with the terminal 
segments divided. The first pair of legs are largely developed, 
and are adapted for seizing hold of different objects, these legs 
terminate with one large claw, three smaller claws branching 
inwards from the large ones, all of which are excessively sharp- 
pointed. There are six smaller legs, the tips of which are very 
sensitive. This creature is also supplied with a single pair of true 
foot jaws called maxillipedes; there are six other foot jaws, 
which I notice are used for swimming, and which are well adapted 
for them purpose; the foot is very much like a small round leaf, 
and presents a good surface against the water for propelling this 
' creature. The eyes, four in number, are su ported upon foot 
stalks, as in decapoda, the sense of sight SIHEN acuto, they 
observe the least movement; the antennæ are remarkably sensi- 
