428 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



The distal end of the thoracic hooks terminates in a thick fang with 

 a crest of 6 well separated teeth in a single, slightly curved row. The 

 hood is long and slender but fits well over the beak ; it has a small aper- 

 ture and long slit (pi. 52, fig. 3). The distal end of abdominal hooks 

 terminates in a long, thick fang and 3 teeth, the middle one slightly 

 higher than the others. It may be supposed that the 6 terminal teeth in 

 thoracic hooks represents a more primitive condition in which they subse- 

 quently fused by twos ; this fusion might result in a tridentate hook. The 

 same pattern is to be observed in H. filobranchus (see below) and may 

 represent a character of generic significance. 



The extensive synonymy of this species is recorded elsewhere (Eisig, 

 1887, p. 839). 



Distribution. — H. filiformis is widely distributed in Western and 

 Eastern Hemispheres; it is common along the eastern shores of North 

 America from New England south at least to Florida ; it occurs especially 

 in mud flat areas. It has been found also in San Francisco Bay, California 

 where 4 individuals were collected in July, 1936; in so far as I know this 

 constitutes the first record from the western shores of the Americas. 



Heteromastus filobranchus Berkeley 

 Plate 5 3, Figs. 1-4 

 Berkeley, 1932, pp. 671-674, figs. 5-7. 



Collections. — Monterey Bay, California in 37 fms (many) ; San 

 Francisco Bay, California in 5%. fms (8). 



Lateral organs are present on the sides of the thorax between the 

 notopodium and neuropodium but nearer the former. Nephridial aper- 

 tures are visible in intersegmental grooves, the first betwen setigerous 

 segments 6 and 7, the last between 10 and 11; they number 5 pairs. 

 There are no visible lateral organs or nephridial pores on the abdomen. 

 The characteristic palmately divided filamentous branchiae in the abdo- 

 men clearly distinguish this species from the nearly related H. filiformis 

 (see above). 



Hooded hooks in the thorax and abdomen are distinct from those in 

 H. filiformis. In the first the crest consists of only 3 teeth in a straight 

 transverse row (pi. 53, fig. 4) instead of 6 teeth. In abdominal hooks 

 the shoulder is thick and rounded, the neck is slender ; the crest consists of 

 a single, straight row of 3 teeth. 



Distribution. — H. filobranchus has remained unreported except 

 through the original description (Berkeley, 1932) based on a collection 



