44 THE AMERICAN NATURALIST. | [Vor. XXXIX. 
delicate, its prisms easily separating from each other at the mar- 
gins, while beyond these at places the mantle was sometimes 
protruded. 
Three other spat oysters were procured on glass in the same 
way, the dates and sizes being: Aug. 19, 1.20 x 1.58 mm.; 
Aug. 22,.55 X .51 mm. ; Aug. 31, .953 x .861 mm. 
Search was made daily for spat on natural marine objects and 
on Sept. 2nd I found the first, on the outer surface of a half- 
grown oyster shell. It measured 2.3 x 2.4 mm., but instead of 
having a pink, red, or brown coloration as one would suspect 
from comparison with the larval or earliest spat stages; Or, 
instead of having a chalky-white appearance as one would judge 
from comparison with the old oysters; it presented a shining, 
dark metallic lustre with a few faint radiallines. From this 
time onwards they were to be found in increasing numbers, and, 
after being once shown them, the deck hands of the government 
‘steamer Ostrea could also find them. Altogether I have 
observed spat oysters on the shells of the oyster, mussel, clam, 
quohog, bar-clam, razor-clam, round whelk, and on stones. The 
objects with which they may be most easily conflicted are the 
young of Crepidula fornicata and colonies of Ralfsia verrucosa. 
At the time of leaving Malpeque, Sept. 20, the largest this year's 
spat I had seen measured 6 mm. in height, had a dark steel 
lustre, radiating ridges or lines, and very thin edges; the whole 
oyster being thin and fitting so solidly against the supporting 
shell as to require some force with a knife-blade to separate it. 
As to the rate of growth my 4th spat oyster on glass was 
obtained Aug. 31, when it measured .953 x .861 mm. and had 
about sixteen gill-filaments. On Sept. 7 it measured 1.261 x 
1.276 mm. and had about twenty-four gill filaments. A week 
later it measured 1.661 x 1.75 3 mm. One might say that it 
doubled its length and height in two weeks. The smallest 
oysters were about the size of one’s thumb nail. I have put 
out wire baskets containing numbers of selected, half-grown, 
living oysters, having black spat attached, to be examined next 
spring. 
MONTREAL, 23 Dec. 1904. 
