426 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



closely sheathing and has a small aperture. It differs from other species 

 of the subgenus as indicated in the key above. 



Holotype. — AHF no. 78; paratypes in the Allan Hancock Foun- 

 dation. 



Type locality. — Beaufort, North Carolina. 



Distribution. — Beaufort, North Carolina, from intertidal zones to a 

 few fathoms, on muddy bottoms. 



Genus HETEROMASTUS Eisig 

 Type H. filiformis (Claparede) 



The thorax consists of 12 segments of which 11 are setigerous; the 

 second to sixth segments are provided with only pointed setae, the seventh 

 to twelfth segments have only long-handled, hooded hooks. The 

 abdomen is provided with only hooded hooks in notopodia and neuro- 

 podia. Branchiae are either filamentous prolongations or vesicular modi- 

 fications of parapodial parts. Genital apertures are limited to the thorax; 

 lateral organs are present on the thorax and anterior abdominal 

 segments. 



The long handled hooks of this genus are of considerable interest 

 because those of the thorax and abdomen, though at first seemingly 

 different from each other, are essentially alike in their principal parts. 

 Each consists of a long shaft with node, shoulder, neck and beak sur- 

 rounded by a hyaline hood, but in thoracic hooks these parts are almost 

 imperceptible except by actual measurement. It seems possible that these 

 thoracic hooks represent primitive forerunners of the more compact, 

 modified hooks farther back. 



Three species of Heteromastus have been described or reported from 

 the Western Hemisphere; they include H. filiformis (Claparede), 

 H. filobranchus Berkeley and H. similis Southern. A fourth species 

 described as Notojnastus gracilis Verrill (1880, p. 180) may also belong 

 to the genus since it has both hooks and setae in the thorax; however, 6 

 ( instead of 5 ) anterior segments were said to have pointed setae. I have 

 seen no individuals from England or vicinity that fulfill this description 

 (see also Hartman, 1942, p. 11). The first 2 species are present in the 

 collections (see below). The third, originally described from a brackish 

 lake in India (Southern, 1921, pp. 640-642) has been reported from 

 fresh water in Uruguay (Monro, 1937, p. 249). In addition, H. gigan- 

 teus Zachs (1933, p. 131) comes from the North Japan Sea. 



