NO. 2 OLGA HARTMAN : SUBMARINE CANYONS 15 



onuphid, Diopatra ornata, which constructs coarse tubes in algal 

 clumps. Nearly all of the 130 species named at this depth are sparse 

 or absent at greater depths. Many of the species are represented by 

 single or few specimens, suggesting that they have their greater con- 

 centrations at higher levels or in different ecological situations. A few, 

 chief of which are Tharyx tesselata with 71 specimens, Prionospio 

 malmgreni with 34, Typosyllis sp. with 24, Alagelona sacculata with 

 21, M. pacifica with 7, and Lumbrineris spp., attain high fre- 

 quency in a sample. A small anemone, JHarenactis sp., with 10, and a 

 brachiopod, Glottidia albida with 41 specimens, are members of the 

 shelf fauna, as are some small mollusks and many amphipods (see 

 ANALYSES). 



An abrupt faunal change occurs at about 177 meters, where are 

 found Maldane sarsi with 58 specimens, Oivenia f. collaris with 58, 

 Chloeia pinnata with 39, Rhodine bitorquata with 31, and Axiothella 

 rubrocincta with 18 specimens in a sample. Onuphids are represented 

 by Onuphis parva with 22 and Nothria iridescens with 25 specimens. 



The capitellid, Heteromastus filobranchus, and an echiuroid, Arhyn- 

 chite sp., never attain the abundance found in Hueneme canyon, but 

 occur most abundantly in depths of 573 and 367 meters. 



From 676 meters down, a deepwater fauna exists; it includes a 

 small capitellid, Decamastus gracilis, an ampharetid, Anobothrus sp., 

 a lumbrinerid, Lumbrineris longensis, a glycerid, Glycera c. branchio- 

 poda, an orbiniid, Califia calida, a flabelligerid, Brada pilosa, a 

 spionid, Spiophanes pallidas, and few other species (see ANALYSES). 



An ophiuroid, A/nphiodia urtica, attains only moderate abundance, 

 in 378 meters with 28 specimens, where it occurs with Chloeia pinnata. 

 Brissopsid urchins exist from 177 m down but are nowhere con- 

 spicuous. In its lowermost levels, at 832 meters, Mugu canyon is 

 impoverished or dead, like Santa Monica basin with which it merges. 



DUME CANYON 



This canyon (Fig. 4) was sampled in depths from 100 m down. 

 One sample was trawled at the head of the canyon, Nov. 20, 1958, 

 by the Hyperion Engineers, centered at ?>3° 58' 45', 118° 46' 50", 

 in 100 to 110 meters. It contained a large shale-rock pitted at the 

 surface. Its exposed surface was nearly covered with serpulid tubes, 

 chiefly Vermiliopsis spp., and the pitted holes resembled those of 

 pholad mollusks and contained nestling ophiuroids, small seastars, a 



