14 
somewhat shorter, the majority of the larger sized ones being between 4 cm. 
and 5 cm. in length although even here one specimen was found 8 cm. in length. 
It may appear from a consideration only of the data given in Table III that if 
the same number of mussels had been measured from Cheynne Passage a similar 
result might have been obtained. This, however, is highly improbable, as the 
samples measured were typical and the mussels were noticeably larger throughout 
the bed. The fact that the deeper parts of the channel were thickly covered 
with mussels in itself would tend to raise the average length of the mussels of 
that bed since the larger ones were found in such locations. What caused such 
a marked difference in the size of the mussels of the two beds I am unprepared 
to say. It is possible that the mussels of the White Head bed may be younger 
than those of Cheynne Passage. Shells have been preserved for further investi- 
gation of this point. 
In general the size of the mussels at Grand Manan appears to be greater 
than in the St. Andrews region, where in 1917 very few were found over 5 cm. 
in length and the greater majority being as pointed out between 2 cm. and 3.5 cm. 
in length. It will be noted also that they are of about the same length. as those © 
found in the better beds at Digby, N.S. 
It is of interest to compare the lengths of the mussels from Cheynne Passage 
and the White Head bed with the general length for the Passamaquoddy Bay 
region as given by Gould (1870), viz., 2 io inches (i.e., approx. 6.2 cm.); 
and also with the findings of Ganong (1885), viz., “in abundance 3% inches 
(i.e., approx. 8.9 cm.) long and even longer.” It will be noted that the size 
for the Grand Manan mussels corresponds very closely to Gould’s general 
length but falls short of the length as given by Ganong. 
In shape the mussels at Grand Manan are of the Digby type, 7.e., deeper 
in proportion to their length than those of the St. Andrews region (Figs. 3 and 
4, Plate I.); as at Digby the mussels near the upper limits of the bed tend 
toward the typical St. Andrews shape (Figs. 1 and 2, Plate I.). 
SECTION 
AGE OF MUSSEL BEDS: 
1. Age of Mussel Beds of St. Andrews Region. 
The age of the mussel beds of the St. Andrews region was definitely deter- 
mined in 1919. This was done by means of the annual ‘‘check marks”’ on the 
shells by which the writer has found it possible not only to determine the age of 
sea-mussels but also their rate of growth during each growing season. 
A mussel bed typical of those of the St. Andrews region is conveniently 
located near the eastern side of the wharf of the Biological Station. This has, 
therefore, been used as a type bed. It is situated in the littoral zone about low- 
water mark and is laid bare at nearly every tide. The mussels studied were 
taken from that portion of the bed lying nearest low-water mark. 
Material was collected for the purpose of determining the age of the mussels 
in this bed July 14, 1919, from a typical portion of it.. This material included 
all the individuals growing on a small area of the bed and was collected before the 
spat of 1919 was conspicuous. The results of the examination of it are as follows: 
28 
