18 



ALLAN HANCOCK PACIFIC EXPEDITIONS 



VOL. 27 



(a genus nearly restricted to the Listriolobus bed on the coastal shelf) 

 4%, Phoronopsis sp. (another characteristic, nearly exclusively limited 

 species) 14%. These taxa, plus others shared with adjacent communi- 

 ties, such as Amphiodia and Pectinaria, comprise 75% of the specimens 

 in the sample (Graph 10). Unlike the Amphiodia community, in which 

 only 6 species regularly comprise more than 50% of the specimens 

 (owing to predominance of Amphiodia), the Listriolobus community 

 commonly requires tabulation of 14 species to comprise 50% of the spec- 

 imens of a sample. The samples in Graph 10 show the extremes of 

 variability, whereas the heart of the community, represented by about 20 

 samples not shown, is more typical of sample 5419. 



10 20 25 30 40 50 60 80 so 100 ix> 125 



Median Diameter in Microns 



250 



Graph 11. Depth-sediment partitioning of community assemblages 

 of submarine canyons based on those samples analyzed for median 

 diameters and those fitting the schematic dominations of graphs 

 7 and 8. 



THE CANYON ASSOCIATIONS 



Selected canyon samples are prearranged in the trellis diagram of 

 Graph 7, and extend from "typical" samples dominated by Pectinaria 

 alone, to Pectinaria with Dentalium, Pectinaria with Capitella, Pecti- 

 naria with AncistrosylHs, then with Chloeia, and one with Ancistrosyl- 

 lis-Chloeia-Maldane together; on the right are samples dominated by 



