230 THE ICE AGE IN CANADA. 



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 Solenensis, 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 epidermis-clad variety of M. 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. arenaria 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 I 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 Eiviere-du-Loup. 



From the accounts of arctic collectors from Fabricius 

 downwards, it would appear that in Greenland, as in 



