NO. 3 HARTMAN: SUBMARINE CANYONS 61 



ring is smooth and followed by 6 segments with setae in notopodia 

 and neuropodia, and 8 segments with long handled hooks in notopodia 

 and neuropodia. 



Redondo en, south wall, in 57 m (1 + ), 542 m (2), north wall, 

 363 m (1 small), axis, 422 m (1), fan, 602 m (1), 715 m (1). 



Coronado en, in 566 m (19), 812 m (4). 



PDasybranchus sp. 

 Redondo en, in 519 m (5). 



Decamastus, new genus 



Type D. gracilis, new species 



This genus differs from Notomastus (see Hartman, 1947, p. 402) 

 in having 10 instead of 11 thoracic setigerous segments. Posterior para- 

 podia are biramous; neuropodia have reduced numbers of hooks and 

 notopodia have few or none. It differs from Mediomastus, which also 

 has 10 thoracic setigers, in having only pointed setae, instead of 

 setae and hooks, in the thorax. 



Decamastus gracilis, new species 



Redondo en, south wall, in 232 m (100 + , HOLOTYPE), north 

 wall, 113 m (4). 



Mugu en, in 676 m (15+), 755 m (2). 



Length of a nearly complete individual, from Sta. 2191-52, is 47 

 mm and width is 1.1 mm in the widest part, or between the second 

 and fourth thoracic segments. The thorax consists of a short, tri- 

 angular prostomium without eyes, a complete peristomial ring which is 

 nearly as wide as the following segment and slightly longer, and 10 

 setigerous segments with only pointed setae. The abdomen is much 

 longer and narrower, and has many more segments. 



The epithelium of the peristomium and first 2 or 3 segments is 

 slightly reticulated ; it is smooth farther back. Median and posterior 

 abdominal segments appear somewhat moniliform and collared be- 

 cause the parapodial ridges are constricted and have narrow, encircling 

 flanges behind the emergence of the setae, whereas the space between 

 successive parapodia is inflated. In cross section the thorax is cylin- 

 drical, anterior abdominal segments are trapezoidal with the longest 

 side ventral, and posteriormost segments are again subcylindrical but 

 slenderer than those in front. 



Thoracic notopodia and neuropodia are similar to one another in 

 having spreading fascicles of distally pointed setae, located at ectal mar- 

 gins and slightly behind the middle of the segment. The transition from 

 thorax to abdomen is marked only by change from setae to long handled 



