.ON THE LARVA AND SPAT OF THE CANADIAN 
OYSTER. 
JOSEPH STAFFORD. 
Upon opening the Marine Biological Station of Canada for last 
summer’s work the acting director, Professor Ramsay Wright, 
assigned to me the diagnosis of bivalve-larvee occurring in the 
plankton. 
The material was collected over the oyster-beds near Curtain 
Island, off Malpeque, P. E. I. Oyster-larvae were first recog- 
nized on the 25th of July from which time they were present 
in the plankton collections until the 1st of Sept. 
The free-swimming, pelagic larva of the oyster possesses à 
characteristic color, brownish-red — suggestive of the soil of its 
native island shores, a shade which enables it to be immediately 
distinguished from every other bivalve-larva with which it is 
associated. The shell is asymmetrical and inequivalve, the left 
valve being larger, more convex, and with a large umbo, the 
right smaller, flatter and with a moderate umbo. The umbos 
have a postero-dorsal position and project backwards and upwards, 
making the shell broader, deeper and squarer behind and tapering 
but rounded in front. The largest measure .358 * .365 mm. in 
length and height, but the height and shape vary according to 
whichever side is turned towards the observer. Larv& as small 
aS .131 x .138 mm. already possess the characteristic shape and 
color. 
The internal structure of the larval oyster offers some inter- 
esting features. We have been accustomed to think of it as 
vastly different from other bivalve-larvz, corresponding to the 
early assumption of a sessile mode of life. This misconception 
is due to lack of observation of plankton stages, embryologists 
having jumped from early veliger or phylembryo to late pro- 
dissoconch or even early nepionic periods. 
When mounted on a slide the larvae are accustomed to remain 
4C 
