326 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



notopodium and neuropodium of a single segment, that the embedded 

 capillary setae (of Sabellaria) or the conspicuous nuchal hooks on the 

 dorsal side (of Idanthyrsus and Lygdamis) represent the notopodium of 

 another segment, and that the neuropodium of the first postoral segment 

 represents its respective ventral portion. The operculum would thus 

 represent the noto- and neuropodium of the first visible segment; the 

 first postoral segment, the neuropodial portion of the second segment. 

 The third visible segment is normal, vrith notopodia and neuropodia in 

 normal relations. These last 2 named segments are herein designated the 

 2 anterior thoracic segments. 



The following nomenclature is used herein. The operculum with its 

 stalk refers to the portion anterior to the oral aperture; it includes the 

 several rows of opercular paleae with the surrounding papillae, the oral 

 tentacles (when present), and palpi. Although it is recognized that 

 opercular paleae are actually in 2 rows (see above), in some genera 

 (Sabellaria and Phragmatopoma) , where outer, middle, and inner rows 

 are visible, they are considered as 3 rows, recognizing, however, that the 

 middle and inner rows are parts of the same series. The thorax is meant 

 to include the portion posterior to the oral aperture; it includes 2 anterior 

 thoracic and 3 (or 4) parathoracic segments, each except the first with 

 biramous appendages, dorsal and ventral cirri, and simple branchiae. The 

 caudal region (=cauda) is the long, cylindrical portion, lacks parapodia 

 or setae, and is believed to represent perhaps many (50 to 60) segments, 

 since the alimentary tract extends throughout its length, and there are 

 internal traces of transverse septa (Wilson, 1929, p. 247). The anal 

 aperture is at its posterior terminus. 



Development. — Larval stages of Sabellariidae are familiar objects in 

 the plankton along the coastal waters of California and the northeast 

 Pacific during many months of the year. Although frequently observed, 

 they have remained entirely unreported except through a recent reference 

 by Rioja (1939, p. 299, figs. 1-5) under the designation of a spionid 

 larva. The stage shown is a chaetosphere, but with metamorphosis ad- 

 vanced so that thoracic paleae and abdominal uncini are already devel- 

 oped. It resembles sabellarian larvae that have been described from other 

 parts of the world by many observers (see Wilson, 1929, p. 221, for 

 review). 



Development of the sabellarian is typical ; it proceeds from a spherical 

 egg, through a pelagic trochophore, a more or less prolonged (perhaps 

 many weeks) larval life, with striking metamorphosis to a sedentary 

 adult. Early larvae of 2 common California species, Phragmatopoma 



