278 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



The first 12 segments are clearly distinguished, since they are pro- 

 vided with laterally projecting parapodia; thereafter the separation from 

 one segment to the next is made out with difficulty, except in the posterior 

 region, where intersegmental furrows are again distinct and uncinigerous 

 tori somewhat elevated. The neural groove (pi. 26, fig. 66) is depressed 

 throughout. 



The first 3 pairs of parapodia are elongate, papillar, increase in size 

 from the first; their setae emerge as distinct, fan-shaped fascicles from 

 the distal end of the papillar notopodium (pi. 26, fig. 67) ; a second has 

 15 or more fine, pointed setae and a minute nephridial papilla near the 

 ventral base. From the fourth (pi. 26, fig. 67) to twelfth setiger noto- 

 podia are thicker and longer, but the setae project only a short distance, 

 as in the first few pairs. They come to have 20 or more setae in a fascicle. 

 An obscure, opaque white, circular plaque, from which the nephridial 

 papilla arises, can be seen at the ventral base of the third; by the fourth 

 it is more conspicuous and continues so through 4 segments, but by the 

 eighth it is smaller and by the ninth, absent. The nephridial papilla, how- 

 ever, is present on all 12 thoracic setigers. Nephridia of the first 3 setigers 

 are greatly prolonged internally, increasing in length from first to third, 

 but by the fourth they are very much shorter. The transition from third 

 to fourth is shown in pi. 26, fig. 67. 



Abdominal setigers number at least 33, but between this setigerous 

 region and the thoracic one there is a smooth, asetigerous length, about 

 equaling the length of 5 or 6 abdominal segments. Abdominal para- 

 podia are small, short, inconspicuous, from which the uncini project 

 slightly; they number 4 or 5 in a fascicle, are long, spindle shaped, taper 

 distally to blunt points, and are seemingly not at all hooked. 



A broken individual from Bodega Lagoon consists of anterior and 

 posterior ends, is torn in the middle, has 12 thoracic segments, 6 segments 

 lacking setae and 47 abdominal setigers ; it may be complete. 



A. occidentalis is unique in having 12 thoracic setigers, at least 33 

 (perhaps 47) abdominal setigers, and an intermediate zone of perhaps 6 

 segments. 



Holotype. — AHF no. 69. 



Type locality. — Inverness, Tomales Bay, California, in mud flats. 



Distribution. — Central California, intertidal. 



Family Sabellidae 

 Key to Species 



1. Thoracic collar entire, with a single incision middorsally ... 2 



Chone 



1. Thoracic collar with lateral, or also ventral, incision ... 3 



