COMMUNITIES OF THE SEA BOTTOM 345 



our nomenclature) would lie between the Echinocardium-Thyasira 

 Biome and the Amphilepsis-Pecten Biome. This ecotone appears to 

 occur between about 50 and 380 meters depth in the Danish waters. 



Haploop's Community {Association or Faciation) . This is a small 

 area northeast of the island of Zealand, omitted from the map. Hap- 

 loop is included here because of its small size and the presence of 

 several predominants of the major community among the Haploops 

 crustaceans. These appear to be another association of the same 

 major community. The arrangement which we venture to present here 

 is in a considerable measure for the purpose of paralleling the phe- 

 nomena found on land. 



Astarte — Area Community (Biome) 



This community is characterized by Astarte crenta, by Area gla- 

 cialis, and also by several of the lamellibranchs and annelids which 

 were also found in the Macoma ealearia community, several species 

 of Portlandia, Cardium, Pecten groenlandiciis, for instance. "This com- 

 munity is described from east Greenland waters, inside the fjords 

 and also in the pack-ice belt at depths from about 50 meters to about 

 250 meters (Sparck, 1933; Thorson, 1934). Further, according to the 

 papers by Zenkevitsch, Brotzky, and Idelson it seems to occur in 

 the central parts of the Barents Sea and in the Kara Sea, and it there- 

 fore appears to occur in arctic seas — in several varieties below the 

 Maeoma ealearia community. It seems also to occur in Ramfjord in 

 northern Norway (Soot-Ryen, 1924)" (cf. Sparck, 1935, 1937). 



Amphilepsis-Pecten Community (Biome) (Fig. 82) 



The Amphilepsis-Pecten community occurs in deeper water, ocean- 

 ward from the Echinocardium-Axinus biome (see map, page 349). A 

 more northerly type termed by Sparck (1935) the Astarte crenata 

 community may perhaps be appropriately called the Astarte-Arca 

 biome. 



Foraminifera Community 



This occurs in deeper water than the preceding as a rule. Some 

 annelids and mollusks are found with the Foraminifera. The ob- 

 servation of Verrill (1871-72) suggests a series of communities east of 

 Massachusetts resembling those west of Dcnmai'k. 



Variations in the Bivalve-Annelid Communities. Two types of 

 variation in composition have been described, and called lociations or 

 faciations, depending on the extent. Jensen (1919) describes the for- 

 mer in the various broads of the Limfjord. In the quotation below, 



