48 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL, 27 



and 478 meters, and thereafter, a gastropod, Mitrella permodesta, 

 accompanied by ampharetid polychaetes or echinoids comprise the bulk 

 of the samples. 



San Diego trench, northern end : Biomasses are low, ranging from 

 less than a gram to more than 9 grams to a square meter. The bulk 

 of the animal mass consists of ophiuroid echinoderms or polychaetes, 

 in depths ranging from 686 to 846 meters. 



La Jolla canyon: — Biomass values, in sampled depths of 79 to 976 

 meters, rerated to grams per square meter, are as follows: 



163.6 gm/ sq.m., in 121 meters. 10.0 gm/ sq.m., in 517 m. 



103.8 gm/ sq.m., in 274 m. 9.6 gm/ sq.m., in 371 m. 



35.0 gm/ sq.m., in 79 m. 5.4 gm/ sq.m., in 793 m. 



22.8 gm/ sq.m., in 976 m. 3.0 gm/ sq.m., in 135 m. 



22.4 gm/ sq.m., in 545 m, negligible, in 708 m. 



10.4 gm/ sq.m., in 637 m. 



The percentages of major animal groups represented in these depths 

 are as follows : 



In 79 meters, with 17.5 grams: 



polychaetes 55.4% 



a nemertean 36.0 

 mollusks 8.6 



In 121 meters, with 81.8 grams: 



shelled mollusks 49.5% 



polychaetes 33.8 



ophiuroids 16.7 



In 135, 274 and 371 meters, with weights 1.5, 36.9 and 4.8 grams 



respectively, polychaetes chiefly Capitella capitata subspp. comprised 



nearly the entire biomass. 



In 517 meters, with 5.0 grams: 



polychaetes 64.0% 



mollusks, chiefly Thyasira 36.0 



In 545 meters, with 1 1.2 grams: 



abrissopsid 68.8% 



polychaetes 22.3 



mollusks 8,9 



In 637 meters, with 5.2 grams: 



shelled mollusks 61.5% 



polychaetes 38,5 



