PLEISTOCENE FOSSILS. 231 



Pleistocene 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 the walrus and other animals, and is 

 much used by the inhabitants. It also appears that a 

 small variety of M. arenaria, with brown epidermis, is 

 most common in Greenland, and occurs with Mija truncata, 

 which is, however, more plentiful. The description given 

 by Fabricius of M. arenaria obviously agrees with that of 

 my small and brown variety from Metis. 



It is interesting to note the companionship of these 

 allied species in the North Atlantic throughout the Pleis- 

 tocene and Modern periods, and the range of varietal 

 forms applicable to each, according to the conditions to 

 which they have been exposed, along with their continued 

 specific distinctness, and the preference of each for certain 

 kinds of environment, so that in some places one, and in 

 others the other, predominates, while this relative predo- 

 minance, as well as the prevalence of certain varietal 

 forms, might no doubt be reversed by change of climate 

 or of depth. 



Mya arenaria. Linu. 



Fossil — Leda clay and lower part of Saxioava sand ; Montreal ; 

 Upton ; Quebec ; Murray Bay ; Labrador ; Duck cove and Lawlor's 

 lake, New Brunswick (Matthew) ; Anticosti ; Goose River ; New 

 Richmond; Tatagouche River, N.B. (Paisley); Gardiner, Maine; 

 Upton, P.Q. ; Portland, Maine ; Greenland (MoUer) ; also in the Post- 

 pliocene of Europe. 



Recent — Little Metis ; Riviere-du-Loup, &c. Very abundant 

 throughout the Gulf of St. Lawrence and coast of Nova Scotia and New 

 England, also Arctic seas generally. Mr. Jeffreys considers it identi- 

 cal with M. Japonica. Jay. This or allied in W. America, I*. P. C. 



In the Gulf this species grows to a large size ; I have a specimen five 

 inches long from Gaspe ; but in the Post-pliocene it is small and often 

 of a short and rounded variety. This is especially the case inland, as 



