Note on Balanus Hamert. 291 
ping the outer limit of M arenaria. The short or Uddevalen- 
sis variety of truncata was, however, very rare, only a few 
shells in a perfectly recent state having been found, and they 
probably lived in somewhat deeper and colder water than 
the others. The water, I may add, on this coast is so far 
affected by the Arctic current as to be quite cold, except 
near the shore and in shallow bays, and the species dredged 
in 10 to 15 fathoms are, in general, similar to those of the 
Labrador coast, belonging rather to the boreal than to the 
Acadian fauna. With the Myas were cast up shells of 
Solen ensis, var. Americanus of Carpenter, and of Machaera 
Costata, the latter sometimes of large size, though it is more 
abundant in the warmer water at the head of the bay, 
where Purpura Lapillus, a rare shell on this coast, also 
occurs on the reefs. 
It is evident that though there is no passage from one 
‘species into the other, the long variety of Mya truncata 
represents the extreme limit of modification of that species 
for a shallow and warm-water habitat, while the small epi- 
dermis-clad variety of MW. arenaria represents its extreme 
modification for deeper and colder water than usual; and 
along the coast at Metis these two varieties meet. 
The coldness of the Pleistocene seas thus explains the 
occurrence, in the Upper Leda clay, of the peculiar small 
and epidermis-clad variety of M. arenario and of the short 
form of Mya truncata. The conditions in the colder parts 
of the River St. Lawrence approach in these respects to 
those of the Pleistocene, though they are no doubt more 
fully realized in the Arctic seas. 
As | have remarked in my notes on the Post Pliocene, 
the brown wrinkled epidermis-clad variety of M. arenaria 
occurs plentifully along with M. Uddevalensis in the Upper 
Leda clay at Riviére du Loup. 
From the accounts of Arctic collectors from Fabricius 
downwards, it would appear that in Greenland, as in Pleis- 
tocene Canada, M. truncata is very abundant, and occurs at 
low water in the sands, as M. arenaria does further south. 
It would seem also that it forms a large part of the food of 
