408 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



provided with hooded hooks only. The abdominal segments have only 

 hooded hooks throughout. Special branchiae are wanting. Lateral 

 organs are present from the first setigerous segment and probably con- 

 tinued throughout. Nephridial apertures are few, limited to posterior 

 thoracic segments. 7"he proboscis is epithelial, it is papillated on its 

 proximal portion and smooth distally. A single species is known. 



Mediomastus californiensis Hartman 

 Plate 46, Figs. 3, 4 

 Hartman, 1944, p. 264. 



Collections. — Numerous individuals come from central California 

 and Oregon, in intertidal zones. 



Lateral organs are present from the first setigerous segment and are 

 continued throughout the thorax; they are located between notopodia and 

 neuropodia and slightly nearer the former. They are continued through 

 abdominal segments in a similar position, but are sometimes difficult to 

 distinguish because of their small size. Nephridial apertures number 

 only 3 pairs; they are first present in the segmental groove between the 

 seventh and eighth, and are continued back to the ninth and tenth, setiger- 

 ous segments. None have been identified in the abdomen. Genital aper- 

 tures are seemingly absent. 



Hooded hooks have a closely fitting hood with a small aperture. The 

 shaft is thick and compact with a gently sloping node. Shoulder and 

 neck regions are well defined. On the beak the fang is thick, strong, 

 and surmounted by 3 well-separated teeth arranged in a triangle as seen 

 in frontal view. The fibrillations of the core extend from the base dis- 

 tally to the beak. 



Distribution. — This is known to occur commonly in intertidal, 

 estuarine zones from Oregon south to central California. It inhabits 

 muddy sand that is fairly compact and fine in composition. 



Genus GAPITITA, new genus 

 Type G. ambiseta, new species 



Pointed setae and hooded hooks are present in both thorax and ab- 

 domen. The first segment is apodous and achaetous; the second to fifth 

 segments are provided with only pointed setae in both notopodia and 

 neuropodia. The sixth to tenth segments have only hooded hooks that 

 resemble those farther back. The eleventh segment is transitional; its 

 parapodia are provided with only hooks. In tlie abdomen the first 8 to 16 



