WIGLEY and STINTON: REMAINS FROM MARINE SEDIMENTS 



The 10 most widely distributed species, in de- 

 creasing order, were: Yoldia sapotilla, Ceras- 

 toderma pinmdatum, Astarte undata, Thyasira 

 trisinnata, Venericardia borealis, Arctica islan- 

 dica, Placopecten magellaniciis, Phacoides filos- 

 us, Crenella glandula, and Nucula proxima. All 

 of these species inhabited rather broad east-west 

 zones across the study area, except for Nucula 

 proxima, which was absent in shallow water 

 in the western sector. Its distribution was 

 alig-ned in the north-south direction, and to some 

 extent east-west. 



Bathymetric distributions differed greatly 

 among various pelecypod species. Depth range 

 in which each species was found is listed in 

 Table 7, and data for the most common species 

 are plotted in Figure 10. Species dispersed over 

 the widest depth range (38 to 567 m) were 

 Astarte imdata and Placopecten magellanicus. 

 Depth ranges of 21 species were very narrow, 

 but nearly all of these were based on few col- 

 lections. Most of the species that occurred in 

 two or more collections were taken over rather 

 broad depth ranges. 



Species found in shallow water (less than 

 50 m) were: Anadara ovalis, Cyrtodaria si- 

 liqua, Liocyma fhictuosa, Lyonsia hyalina, Modi- 

 olus demissus, Mytilus edulis, Siliqua costata, 

 and Tellina agilis. 



Species found in deep water (taken at depths 

 greater than 200 m) were: Anomia aculeata, 

 Astarte subequilatera, A. undata, Cerastoderyna 

 pinnulatum, Limatula subauriculata, Nucula 

 proxima, N. temtis, Nuculana acuta, Phacoides 

 blakeansis, P. filosus, Placopecten magellanicus, 

 Thyasira plana, T. trisinuata, Vene7'ica7^dia bo- 

 realis, and Yoldia sapotilla. 



Density of shells of individual pelecypod spe- 

 cies ranged from 10/m- to 4,600 /m- (Table 4). 

 Densities tended to be high for the more widely 

 distributed species and low for species with a re- 

 stricted geographic distribution. Species found 

 in greatest density were: Venericardia borealis 

 — 4,600/m-, Arctica islandica — 2,080/m-, As- 

 tarte subequilatera — 1,560/m-, Nucula proxima 

 — 1,360/m-, Asta^'te undata — 1,440/m-, and 

 Thyasira trisinuata — 1,160/m^ All of these, 

 except Astarte subequilatera, were among the 

 10 species with the widest geographic distribu- 



Table 7. — Bathymetric distributions of 57 species of 

 pelecypods and the number of stations at which each 

 occurred. 



tion. Among the species collected at 10 stations 

 or less, few occurred in densities greater than 



15 



